feat(dashboard): expand themes to fonts, layout, density (#14725)

Dashboard themes now control typography and layout, not just colors.
Each built-in theme picks its own fonts, base size, radius, and density
so switching produces visible changes beyond hue.

Schema additions (per theme):

- typography — fontSans, fontMono, fontDisplay, fontUrl, baseSize,
  lineHeight, letterSpacing. fontUrl is injected as <link> on switch
  so Google/Bunny/self-hosted stylesheets all work.
- layout — radius (any CSS length) and density
  (compact | comfortable | spacious, multiplies Tailwind spacing).
- colorOverrides (optional) — pin individual shadcn tokens that would
  otherwise derive from the palette.

Built-in themes are now distinct beyond palette:

- default  — system stack, 15px, 0.5rem radius, comfortable
- midnight — Inter + JetBrains Mono, 14px, 0.75rem, comfortable
- ember    — Spectral (serif) + IBM Plex Mono, 15px, 0.25rem
- mono     — IBM Plex Sans + Mono, 13px, 0 radius, compact
- cyberpunk— Share Tech Mono everywhere, 14px, 0 radius, compact
- rose     — Fraunces (serif) + DM Mono, 16px, 1rem, spacious

Also fixes two bugs:

1. Custom user themes silently fell back to default. ThemeProvider
   only applied BUILTIN_THEMES[name], so YAML files in
   ~/.hermes/dashboard-themes/ showed in the picker but did nothing.
   Server now ships the full normalised definition; client applies it.
2. Docs documented a 21-token flat colors schema that never matched
   the code (applyPalette reads a 3-layer palette). Rewrote the
   Themes section against the actual shape.

Implementation:

- web/src/themes/types.ts: extend DashboardTheme with typography,
  layout, colorOverrides; ThemeListEntry carries optional definition.
- web/src/themes/presets.ts: 6 built-ins with distinct typography+layout.
- web/src/themes/context.tsx: applyTheme() writes palette+typography+
  layout+overrides as CSS vars, injects fontUrl stylesheet, fixes the
  fallback-to-default bug via resolveTheme(name).
- web/src/index.css: html/body/code read the new theme-font vars;
  --radius-sm/md/lg/xl derive from --theme-radius; --spacing scales
  with --theme-spacing-mul so Tailwind utilities shift with density.
- hermes_cli/web_server.py: _normalise_theme_definition() parses loose
  YAML (bare hex strings, partial blocks) into the canonical wire
  shape; /api/dashboard/themes ships full definitions for user themes.
- tests/hermes_cli/test_web_server.py: 16 new tests covering the
  normaliser and discovery (rejection cases, clamping, defaults).
- website/docs/user-guide/features/web-dashboard.md: rewrite Themes
  section with real schema, per-model tables, full YAML example.

tests/hermes_cli/test_web_server.py

@@ -1256,3 +1256,187 @@ class TestStatusRemoteGateway:
         assert data["gateway_running"] is True
         assert data["gateway_pid"] is None
         assert data["gateway_state"] == "running"
+
+
+# ---------------------------------------------------------------------------
+# Dashboard theme normaliser tests
+# ---------------------------------------------------------------------------
+
+
+class TestNormaliseThemeDefinition:
+    """Tests for _normalise_theme_definition() — parses YAML theme files."""
+
+    def test_rejects_missing_name(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        assert _normalise_theme_definition({}) is None
+        assert _normalise_theme_definition({"name": ""}) is None
+        assert _normalise_theme_definition({"name": "   "}) is None
+
+    def test_rejects_non_dict(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        assert _normalise_theme_definition("string") is None
+        assert _normalise_theme_definition(None) is None
+        assert _normalise_theme_definition([1, 2, 3]) is None
+
+    def test_loose_colors_shorthand(self):
+        """Bare hex strings under `colors` parse as {hex, alpha=1.0}."""
+        from hermes_cli.web_server import _normalise_theme_definition
+        result = _normalise_theme_definition({
+            "name": "loose",
+            "colors": {"background": "#000000", "midground": "#ffffff"},
+        })
+        assert result is not None
+        assert result["palette"]["background"] == {"hex": "#000000", "alpha": 1.0}
+        assert result["palette"]["midground"] == {"hex": "#ffffff", "alpha": 1.0}
+        # foreground falls back to default (transparent white)
+        assert result["palette"]["foreground"]["hex"] == "#ffffff"
+        assert result["palette"]["foreground"]["alpha"] == 0.0
+
+    def test_full_palette_form(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        result = _normalise_theme_definition({
+            "name": "full",
+            "palette": {
+                "background": {"hex": "#0a1628", "alpha": 1.0},
+                "midground": {"hex": "#a8d0ff", "alpha": 0.9},
+                "warmGlow": "rgba(255, 0, 0, 0.5)",
+                "noiseOpacity": 0.5,
+            },
+        })
+        assert result["palette"]["background"]["hex"] == "#0a1628"
+        assert result["palette"]["midground"]["alpha"] == 0.9
+        assert result["palette"]["warmGlow"] == "rgba(255, 0, 0, 0.5)"
+        assert result["palette"]["noiseOpacity"] == 0.5
+
+    def test_default_typography_applied_when_missing(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        result = _normalise_theme_definition({"name": "minimal"})
+        typo = result["typography"]
+        assert "fontSans" in typo
+        assert "fontMono" in typo
+        assert typo["baseSize"] == "15px"
+        assert typo["lineHeight"] == "1.55"
+        assert typo["letterSpacing"] == "0"
+
+    def test_partial_typography_merges_with_defaults(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        result = _normalise_theme_definition({
+            "name": "partial",
+            "typography": {
+                "fontSans": "MyFont, sans-serif",
+                "baseSize": "12px",
+            },
+        })
+        assert result["typography"]["fontSans"] == "MyFont, sans-serif"
+        assert result["typography"]["baseSize"] == "12px"
+        # fontMono defaulted
+        assert "monospace" in result["typography"]["fontMono"]
+
+    def test_layout_defaults(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        result = _normalise_theme_definition({"name": "minimal"})
+        assert result["layout"]["radius"] == "0.5rem"
+        assert result["layout"]["density"] == "comfortable"
+
+    def test_invalid_density_falls_back(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        result = _normalise_theme_definition({
+            "name": "bad",
+            "layout": {"density": "ultra-spacious"},
+        })
+        assert result["layout"]["density"] == "comfortable"
+
+    def test_valid_densities_accepted(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        for d in ("compact", "comfortable", "spacious"):
+            r = _normalise_theme_definition({"name": "x", "layout": {"density": d}})
+            assert r["layout"]["density"] == d
+
+    def test_color_overrides_filter_unknown_keys(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        result = _normalise_theme_definition({
+            "name": "o",
+            "colorOverrides": {
+                "card": "#123456",
+                "fakeToken": "#abcdef",
+                "primary": 42,  # non-string rejected
+                "destructive": "#ff0000",
+            },
+        })
+        assert result["colorOverrides"] == {
+            "card": "#123456",
+            "destructive": "#ff0000",
+        }
+
+    def test_color_overrides_omitted_when_empty(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        result = _normalise_theme_definition({"name": "x"})
+        assert "colorOverrides" not in result
+
+    def test_alpha_clamped_to_unit_range(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        r = _normalise_theme_definition({
+            "name": "c",
+            "palette": {"background": {"hex": "#000", "alpha": 99.5}},
+        })
+        assert r["palette"]["background"]["alpha"] == 1.0
+        r2 = _normalise_theme_definition({
+            "name": "c",
+            "palette": {"background": {"hex": "#000", "alpha": -5}},
+        })
+        assert r2["palette"]["background"]["alpha"] == 0.0
+
+    def test_invalid_alpha_uses_default(self):
+        from hermes_cli.web_server import _normalise_theme_definition
+        r = _normalise_theme_definition({
+            "name": "c",
+            "palette": {"background": {"hex": "#000", "alpha": "not a number"}},
+        })
+        assert r["palette"]["background"]["alpha"] == 1.0
+
+
+class TestDiscoverUserThemes:
+    """Tests for _discover_user_themes() — scans ~/.hermes/dashboard-themes/."""
+
+    def test_returns_empty_when_dir_missing(self, tmp_path, monkeypatch):
+        monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+        from hermes_cli import web_server
+        assert web_server._discover_user_themes() == []
+
+    def test_loads_and_normalises_yaml(self, tmp_path, monkeypatch):
+        monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+        themes_dir = tmp_path / "dashboard-themes"
+        themes_dir.mkdir()
+        (themes_dir / "ocean.yaml").write_text(
+            "name: ocean\n"
+            "label: Ocean\n"
+            "palette:\n"
+            "  background:\n"
+            "    hex: \"#0a1628\"\n"
+            "    alpha: 1.0\n"
+            "layout:\n"
+            "  density: spacious\n"
+        )
+        from hermes_cli import web_server
+        results = web_server._discover_user_themes()
+        assert len(results) == 1
+        assert results[0]["name"] == "ocean"
+        assert results[0]["label"] == "Ocean"
+        assert results[0]["palette"]["background"]["hex"] == "#0a1628"
+        assert results[0]["layout"]["density"] == "spacious"
+        # defaults filled in
+        assert "fontSans" in results[0]["typography"]
+
+    def test_malformed_yaml_skipped(self, tmp_path, monkeypatch):
+        monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+        themes_dir = tmp_path / "dashboard-themes"
+        themes_dir.mkdir()
+        (themes_dir / "bad.yaml").write_text("::: not valid yaml :::\n\tindent wrong")
+        (themes_dir / "nameless.yaml").write_text("label: No Name Here\n")
+        (themes_dir / "ok.yaml").write_text("name: ok\n")
+        from hermes_cli import web_server
+        results = web_server._discover_user_themes()
+        names = [r["name"] for r in results]
+        assert "ok" in names
+        assert "bad" not in names  # malformed YAML
+        assert len(results) == 1  # only the valid one