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.

.gitignore

@@ -33,6 +33,10 @@ web-build/
 apps/desktop/out/
 apps/desktop/release/
 
+# Bundle visualizer reports
+apps/desktop/stats.html
+apps/desktop/stats.json
+
 # Logs
 *.log
 npm-debug.log*