perf(P6C.T11): bundle audit + opt-in visualizer for future audits

Audited the renderer bundle with rollup-plugin-visualizer. Top offenders
(libsodium-sumo 292KB gz, livekit-client 177KB gz, @supabase 149KB gz)
all have justified usage and no viable swap. Mediapipe + track-processors
are already lazy-loaded into a separate chunk on first BackgroundBlur
activation. Bundle has zero duplicate packages, no moment/lodash/dayjs,
no syntax-highlight libs, no polyfills — already lean from T1+T6.

Added rollup-plugin-visualizer as a dev-dep, gated behind ANALYZE=true
so production builds pay no cost. Run with:
  ANALYZE=true pnpm --filter @chat-app/desktop build
to regenerate stats.html (treemap) + stats.json (raw) for future audits.

apps/desktop/electron.vite.config.ts

@@ -10,6 +10,9 @@
 import react from '@vitejs/plugin-react';
 import { defineConfig, externalizeDepsPlugin } from 'electron-vite';
 import path from 'node:path';
+import { visualizer } from 'rollup-plugin-visualizer';
+
+const ANALYZE = process.env.ANALYZE === 'true';
 
 const rendererAliases = {
   '@': path.resolve(__dirname, './src'),
@@ -44,7 +47,30 @@ export default defineConfig({
     // bundle. Relative base produces `./assets/...` which works in both
     // dev (served from /) and packaged builds.
     base: './',
-    plugins: [react()],
+    // Visualizer plugins are gated behind ANALYZE=true so the production
+    // build never pays the analysis cost. Re-enable with:
+    //   ANALYZE=true pnpm --filter @chat-app/desktop build
+    // which writes apps/desktop/stats.html (treemap) + stats.json (raw).
+    plugins: [
+      react(),
+      ...(ANALYZE
+        ? [
+            visualizer({
+              filename: 'stats.html',
+              template: 'treemap',
+              gzipSize: true,
+              brotliSize: true,
+              open: false,
+            }),
+            visualizer({
+              filename: 'stats.json',
+              template: 'raw-data',
+              gzipSize: true,
+              brotliSize: true,
+            }),
+          ]
+        : []),
+    ],
     resolve: {
       alias: rendererAliases,
     },