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/src/components/ErrorBoundary.tsx

@@ -1,7 +1,7 @@
 import type { ReactNode } from "react";
 import i18n from "../i18n";
 import { notify } from "../lib/notifications";
-import { CrashBoundary, type CrashCopy } from "./CrashBoundary";
+import { CrashBoundary, type CrashCopy } from "./ui/CrashBoundary";
 
 const copy = (): CrashCopy => ({
   title: i18n.t("errors.boundary.title"),