fix(gate): knip sees the watch entry, the build must emit watch.html, and two hand copies are held

- The raw-source contract tests read files from disk (rawSources.testkit)
  instead of import.meta.glob, which knip counted as importing every src file —
  its unused-files lane could never name an orphan. knip now names
  src/watchMain.tsx as an entry (registered in docs/gates.md).
- vite build fails when index.html or watch.html is not emitted.
- The watch-entry import walk follows dynamic import() too.
- audit_metrics.py's plan-code patterns are held equal to the guard's.
- CrashBoundary is domain-free: it moves into components/ui.

frontend/knip.jsonc

@@ -1,5 +1,7 @@
 {
   "$schema": "https://unpkg.com/knip@6/schema.json",
+  // The shared link's page (watch.html): the Vite plugin reads only index.html for entries.
+  "entry": ["src/watchMain.tsx"],
   "project": ["**/*.{ts,tsx,js}"],
   "playwright": {
     "config": ["playwright.config.ts"],