build(patch-package): backport vitest PR #10267 for browser-playwright birpc race

Installs patch-package (^8.0.0) and a postinstall script, then applies
the diff from vitest PR #10267 against @vitest/browser-playwright@4.1.0.

What the patch changes (in dist/index.js):

- createPredicate(sessionId, url) → createPredicate(url): factory becomes
  pure, returns { url, predicate } instead of mutating sessionIds /
  idPreficates as a side-effect.
- sessionIds value type: array → Set (deduplicates resolved URLs).
- register handler now looks up any existing predicate for the
  (sessionId, resolvedUrl) pair and unroutes it BEFORE installing the
  new route. This is the actual race fix: without it, the second
  vi.mock for a duplicate-id leaks an orphan Playwright route that
  fires after birpc closes.
- clear handler iterates the Set via spread.

Why this matters even though Layer 1 normalised the only known duplicate
in our suite: every future vi.mock call is a class of race we shouldn't
have to think about. The patch closes the upstream gap at the
route-handler level, so a contributor reintroducing the duplicate-id
pattern can't reopen the race.

When to remove: when @vitest/browser-playwright ships a release
containing PR #10267. Delete patches/@vitest+browser-playwright+4.1.0.patch
and the postinstall hook (or keep the hook if other patches accumulate).

Refs: #553 · vitest-dev/vitest#9957 · vitest-dev/vitest#10267

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -8,6 +8,7 @@
 		"build": "vite build",
 		"preview": "vite preview",
 		"prepare": "svelte-kit sync || true && git -C .. config core.hooksPath .husky 2>/dev/null || true",
+		"postinstall": "patch-package",
 		"check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
 		"check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch",
 		"format": "prettier --write .",
@@ -54,6 +55,7 @@
 		"eslint-plugin-svelte": "^3.13.0",
 		"globals": "^16.5.0",
 		"openapi-typescript": "^7.8.0",
+		"patch-package": "^8.0.0",
 		"playwright": "^1.56.1",
 		"prettier": "^3.6.2",
 		"prettier-plugin-svelte": "^3.4.0",