perf(api,web,db): refactor and optimize for enterprise readiness

- Add missing @@index([userId]) on Account and Session models (auth query perf)
- Batch holiday-auto-import to eliminate N+1 query pattern (O(n) → O(1))
- Reduce SessionProvider refetchInterval from 5min to 15min
- Fix Cache-Control catch-all to stop blocking static asset caching
- Decompose assistant-tools.ts (2,562 → 809 lines) into callers, helpers, access-control modules
- Add @next/bundle-analyzer for data-driven bundle optimization
- Add @react-pdf/renderer to optimizePackageImports
- Add safety caps (take limits) on unbounded findMany queries

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/package.json

@@ -49,6 +49,7 @@
     "zod": "^3.23.8"
   },
   "devDependencies": {
+    "@next/bundle-analyzer": "^15.5.15",
     "@axe-core/playwright": "^4.11.1",
     "@capakraken/eslint-config": "workspace:*",
     "@capakraken/tsconfig": "workspace:*",