opentui(phase3): launcher integration — HERMES_TUI_ENGINE dual-engine

hermes --tui launches the native OpenTUI engine (Bun) when
HERMES_TUI_ENGINE=opentui (env) or display.tui_engine=opentui (config);
Ink stays the default and the shipping path is untouched.

- _resolve_tui_engine() (env > config > ink); refuses opentui on
  Windows/Termux (no Bun) -> falls back to ink with a notice.
- _make_opentui_argv() -> [bun, src/entry.real.tsx] (no build step).
- _bun_bin() with HERMES_BUN override.
- Branch at top of _make_tui_argv BEFORE _ensure_tui_node (Bun-only host
  must not bootstrap Node).
- Gate _launch_tui NODE_OPTIONS/--max-old-space-size on engine==ink (Bun
  is JSC; the V8 flag errors/ignores).

Verified end-to-end via tmux: real hermes --tui -> Bun -> OpenTUI ->
real Python gateway streamed a real reply. No-flag default still ink.

tests/scripts/test_build_skills_index_health.py

@@ -1,99 +0,0 @@
-"""Invariants for scripts/build_skills_index.py's health-check guard.
-
-Regression context (June 2026): a GitHub API rate limit zeroed every
-api.github.com-backed source (github / claude-marketplace / well-known) at
-once during the docs deploy crawl. The build's health check fired and exited
-non-zero — but it had ALREADY written the degenerate index to disk, and
-deploy-site.yml swallowed the exit code with ``|| echo non-fatal``. The
-partial index (missing the OpenAI/Anthropic/HuggingFace/NVIDIA tabs) shipped
-to the live Skills Hub.
-
-These tests pin the two contracts that prevent a recurrence:
-  1. A degenerate crawl exits non-zero AND does NOT write the output file
-     (so extract-skills.py falls back instead of reading a broken index).
-  2. A healthy crawl exits zero AND writes the file with every source present.
-"""
-
-import os
-import sys
-import types
-
-import pytest
-
-import scripts.build_skills_index as build_mod
-
-
-def _meta(name, src):
-    return build_mod.SkillMeta(
-        name=name, description="d", source=src,
-        identifier=f"{src}/{name}", trust_level="community",
-    )
-
-
-class _FakeSource:
-    def __init__(self, src, n, rate_limited=False):
-        self._src = src
-        self._n = n
-        self.is_rate_limited = rate_limited
-
-    def search(self, query, limit=10):
-        return [_meta(f"{self._src}-{i}", self._src) for i in range(self._n)]
-
-
-def _install_fake_sources(monkeypatch, *, github_count, claude_count=40,
-                          well_known_count=10, github_rate_limited=False):
-    monkeypatch.setattr(build_mod, "SkillsShSource", lambda auth: _FakeSource("skills.sh", 15000))
-    monkeypatch.setattr(build_mod, "OptionalSkillSource", lambda: _FakeSource("official", 95))
-    monkeypatch.setattr(build_mod, "WellKnownSkillSource", lambda: _FakeSource("well-known", well_known_count))
-    monkeypatch.setattr(
-        build_mod, "GitHubSource",
-        lambda auth: _FakeSource("github", github_count, rate_limited=github_rate_limited),
-    )
-    monkeypatch.setattr(build_mod, "ClawHubSource", lambda: _FakeSource("clawhub", 69000))
-    monkeypatch.setattr(
-        build_mod, "ClaudeMarketplaceSource",
-        lambda auth: _FakeSource("claude-marketplace", claude_count, rate_limited=github_rate_limited),
-    )
-    monkeypatch.setattr(build_mod, "LobeHubSource", lambda: _FakeSource("lobehub", 500))
-    monkeypatch.setattr(build_mod, "BrowseShSource", lambda: _FakeSource("browse-sh", 380))
-    monkeypatch.setattr(
-        build_mod, "crawl_skills_sh",
-        lambda source: [build_mod._meta_to_dict(m) for m in source.search("", 0)],
-    )
-    monkeypatch.setattr(build_mod, "batch_resolve_paths", lambda skills, auth: skills)
-    monkeypatch.setattr(
-        build_mod, "GitHubAuth",
-        lambda: types.SimpleNamespace(auth_method=lambda: "token"),
-    )
-
-
-def test_degenerate_crawl_exits_nonzero_and_writes_no_file(tmp_path, monkeypatch):
-    """A collapsed GitHub crawl must fail loud and leave OUTPUT_PATH unwritten."""
-    out = tmp_path / "skills-index.json"
-    monkeypatch.setattr(build_mod, "OUTPUT_PATH", str(out))
-    _install_fake_sources(monkeypatch, github_count=0, claude_count=0,
-                          well_known_count=0, github_rate_limited=True)
-
-    with pytest.raises(SystemExit) as exc:
-        build_mod.main()
-
-    assert exc.value.code != 0
-    # The degenerate index must NOT have been written — extract-skills.py
-    # relies on the file's absence to fall back instead of reading garbage.
-    assert not out.exists()
-
-
-def test_healthy_crawl_writes_index_with_all_sources(tmp_path, monkeypatch):
-    out = tmp_path / "skills-index.json"
-    monkeypatch.setattr(build_mod, "OUTPUT_PATH", str(out))
-    _install_fake_sources(monkeypatch, github_count=200)
-
-    build_mod.main()  # exit 0 (no SystemExit)
-
-    assert out.exists()
-    import json
-    data = json.loads(out.read_text())
-    sources = {s["source"] for s in data["skills"]}
-    # Every GitHub-API-backed source that vanished in the regression is present.
-    assert {"github", "claude-marketplace", "well-known"} <= sources
-    assert data["skill_count"] == len(data["skills"])