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/src/lib/trpc/provider.tsx

@@ -89,7 +89,7 @@ export function TRPCProvider({ children }: { children: React.ReactNode }) {
   );
 
   return (
-    <SessionProvider refetchInterval={5 * 60}>
+    <SessionProvider refetchInterval={15 * 60}>
       <trpc.Provider client={trpcClient} queryClient={queryClient}>
         <QueryClientProvider client={queryClient}>{children}</QueryClientProvider>
       </trpc.Provider>