feat(dashboard): always enable embedded chat; remove dashboard --tui flag

The dashboard's embedded Chat surface (/chat, /api/ws, /api/pty) was gated
behind `hermes dashboard --tui` / HERMES_DASHBOARD_TUI=1. The desktop app and
the dashboard's own Chat tab both drive the agent over the /api/ws + /api/pty
WebSockets, so a dashboard started without the flag would pass the /api/status
health check but slam the chat WebSocket shut with WS code 4403 — the app
connects, reports "ready", and chat stays dead. This was the root cause behind
multiple user reports of the desktop app failing to connect to a self-hosted
gateway/dashboard, and it bit Docker and host installs alike.

Make the embedded chat unconditional:

- web_server.py: _DASHBOARD_EMBEDDED_CHAT_ENABLED defaults to True; drop the
  embedded_chat parameter and the runtime reassignment from start_server().
  The WS gates still read the constant (now always true) so the seam — and its
  "rejects when disabled" contract test — stays meaningful.
- main.py: remove the `--tui` argument from the dashboard subparser and the
  `embedded_chat = args.tui or HERMES_DASHBOARD_TUI==1` derivation.
- web/: isDashboardEmbeddedChatEnabled() returns true unconditionally; drop the
  deprecated __HERMES_DASHBOARD_TUI__ alias and the dead LEGACY_TUI_RE scrape in
  the vite dev-token plugin.
- apps/desktop/electron/main.cjs: drop `--tui` from the spawned dashboardArgs
  (it would now error with "unrecognized arguments: --tui") and the redundant
  HERMES_DASHBOARD_TUI env injection.
- Docker: no s6 run-script change needed — the script never passed --tui; the
  HERMES_DASHBOARD_TUI env var is now simply a no-op, so the image works out of
  the box with no extra var.
- Docs: remove every dashboard --tui / HERMES_DASHBOARD_TUI reference across the
  CLI reference, env-var reference, docker/desktop/web-dashboard guides, in-app
  tips, and the zh-Hans translations. The terminal `hermes --tui` / HERMES_TUI
  references are intentionally left untouched.

Tests: 270 passing across web_server, dashboard lifecycle, host-header,
auth-gate, and docker-override-scripts suites.

hermes_cli/web_server.py

@@ -135,9 +135,13 @@ app = FastAPI(title="Hermes Agent", version=__version__, lifespan=_lifespan)
 _SESSION_TOKEN = os.environ.get("HERMES_DASHBOARD_SESSION_TOKEN") or secrets.token_urlsafe(32)
 _SESSION_HEADER_NAME = "X-Hermes-Session-Token"
 
-# In-browser Chat tab (/chat, /api/pty, …).  Off unless ``hermes dashboard --tui``
-# or HERMES_DASHBOARD_TUI=1.  Set from :func:`start_server`.
-_DASHBOARD_EMBEDDED_CHAT_ENABLED = False
+# In-browser Chat tab (/chat, /api/pty, /api/ws, …).  Always enabled: the
+# desktop app and the dashboard's own Chat tab both drive the agent over the
+# `/api/ws` + `/api/pty` WebSockets, so the embedded-chat surface is an
+# unconditional part of the dashboard.  Kept as a module-level constant (rather
+# than inlining ``True`` at every gate) so the WS endpoints and the SPA token
+# injection share a single, testable seam.
+_DASHBOARD_EMBEDDED_CHAT_ENABLED = True
 
 # Simple rate limiter for the reveal endpoint
 _reveal_timestamps: List[float] = []
@@ -8677,15 +8681,10 @@ def start_server(
     port: int = 9119,
     open_browser: bool = True,
     allow_public: bool = False,
-    *,
-    embedded_chat: bool = False,
 ):
     """Start the web UI server."""
     import uvicorn
 
-    global _DASHBOARD_EMBEDDED_CHAT_ENABLED
-    _DASHBOARD_EMBEDDED_CHAT_ENABLED = embedded_chat
-
     # Phase 0: stash the auth-gate flag on app.state so middleware / SPA-token
     # injection / WS-auth paths can branch on it consistently.  Phase 3.5
     # uses this to decide whether to refuse the bind, log the gate-on