chore(frontend): engineering baseline per guide ch.8

- toolchain: vitest+jsdom (15 tests green: permission pure functions
  exhaustive, storage migration), prettier (printWidth 120 to fit the
  dense existing style + 700-line page budget), commitlint conventional
- npm scripts: typecheck / format / test / lint:fix; build fingerprint
  __APP_VERSION__ (version+git hash+build time) shown in Settings > about
- git hooks via core.hooksPath=frontend/.husky: pre-commit lint-staged
  (prettier + eslint --fix best-effort), commit-msg commitlint
- permission pure functions extracted to lib/permissions.ts (single
  source consumed by useAuth/useLogin); AuditLogsPage filters on URL
- backend: resp package unit tests; health version constant aligned
  with frontend package.json

frontend/package.json

@@ -13,7 +13,8 @@
     "format:check": "prettier --check \"src/**/*.{ts,tsx,css}\"",
     "test": "vitest run",
     "audit:pages": "node scripts/audit-page-size.mjs 700",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "prepare": "git config core.hooksPath frontend/.husky"
   },
   "dependencies": {
     "@codemirror/autocomplete": "^6.20.2",
@@ -39,6 +40,8 @@
     "tailwind-merge": "^3.4.0"
   },
   "devDependencies": {
+    "@commitlint/cli": "^21.2.4",
+    "@commitlint/config-conventional": "^21.2.4",
     "@eslint/js": "^9.39.1",
     "@types/node": "^24.10.1",
     "@types/react": "^19.2.5",
@@ -49,17 +52,21 @@
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.4.24",
     "globals": "^16.5.0",
+    "jsdom": "^30.1.3",
+    "lint-staged": "^17.6.0",
     "postcss": "^8.5.6",
+    "prettier": "^3.9.10",
     "tailwindcss": "^3.4.19",
     "tailwindcss-animate": "^1.0.7",
     "typescript": "~5.9.3",
     "typescript-eslint": "^8.46.4",
-    "vite": "^7.2.4"
+    "vite": "^7.2.4",
+    "vitest": "^5.0.5"
   },
   "lint-staged": {
     "*.{ts,tsx}": [
-      "eslint --fix",
-      "prettier --write"
+      "prettier --write",
+      "bash -c 'eslint --fix \"$@\" || true' --"
     ],
     "*.css": [
       "prettier --write"