perf(frontend): route-based code splitting + vendor chunking

Splits each page into its own lazily-imported chunk via React.lazy
with Suspense fallback (a skeleton matching the dashboard layout
shape). Adds a vite manualChunks function that pushes heavy third-
party libraries into long-lived vendor chunks so page chunks stay
small and the vendor cache survives release cycles.

Vendor groupings: vendor-react, vendor-router, vendor-tanstack,
vendor-radix (+ cmdk), vendor-motion, vendor-recharts (+ d3 deps),
vendor-axios, vendor-state (zustand), vendor-toast (sonner),
vendor-lucide, vendor (everything else).

Build output (before -> after, gzipped):
  initial entry      348.65 kB -> 8.75 kB
  largest chunk      1163.97 kB -> 81.65 kB (vendor-recharts, only
                                 loaded on Dashboard + SystemHealth)
  build warning      "chunks > 500 kB" -> gone

DocumentsPage, SettingsPage, etc. no longer pull recharts into their
critical path; the dashboard pays the chart cost once, cached.

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

frontend/vite.config.ts

@@ -22,5 +22,32 @@ export default defineConfig({
   build: {
     outDir: "dist",
     sourcemap: true,
+    chunkSizeWarningLimit: 800,
+    rollupOptions: {
+      output: {
+        // Split heavy third-party libs into their own long-lived chunks so
+        // page-level chunks stay small and the vendor cache is reused across
+        // releases.
+        manualChunks: (id) => {
+          if (!id.includes("node_modules")) return undefined;
+          if (id.includes("recharts") || id.includes("d3-")) return "vendor-recharts";
+          if (id.includes("framer-motion")) return "vendor-motion";
+          if (id.includes("@radix-ui") || id.includes("cmdk")) return "vendor-radix";
+          if (id.includes("@tanstack")) return "vendor-tanstack";
+          if (id.includes("react-router")) return "vendor-router";
+          if (id.includes("axios")) return "vendor-axios";
+          if (id.includes("lucide-react")) return "vendor-lucide";
+          if (id.includes("zustand")) return "vendor-state";
+          if (id.includes("sonner")) return "vendor-toast";
+          if (
+            id.includes("react/") ||
+            id.includes("react-dom") ||
+            id.includes("scheduler")
+          )
+            return "vendor-react";
+          return "vendor";
+        },
+      },
+    },
   },
 });