feat: maximize Sentry free plan coverage for frontend and backend

- ErrorBoundary: use Sentry.ErrorBoundary with crash feedback dialog
- RouteError: capture route errors in Sentry (skip chunk load errors)
- User context: set Sentry user on login (frontend + backend)
- Backend: enable profiling (profiles_sample_rate)
- Frontend: add feedback integration, lower replay rate to conserve quota
- Add temporary verification message for production validation

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

frontend/src/instrument.ts

@@ -10,6 +10,11 @@ Sentry.init({
       maskAllText: false,
       blockAllMedia: false,
     }),
+    // Crash feedback dialog — prompts users after unhandled errors
+    Sentry.feedbackIntegration({
+      autoInject: false,
+      colorScheme: "dark",
+    }),
   ],
 
   // Tracing — capture 100% in dev, 20% in production
@@ -19,7 +24,13 @@ Sentry.init({
     /^https:\/\/api\.resolutionflow\.com/,
   ],
 
-  // Session Replay — record 10% of sessions, 100% of error sessions
-  replaysSessionSampleRate: 0.1,
+  // Session Replay — conserve free-plan quota
+  // 1% of normal sessions, 100% of error sessions
+  replaysSessionSampleRate: import.meta.env.PROD ? 0.01 : 0.0,
   replaysOnErrorSampleRate: 1.0,
 });
+
+// TODO: Remove after verifying Sentry is receiving frontend events
+if (import.meta.env.PROD) {
+  Sentry.captureMessage("ResolutionFlow frontend Sentry verification", "info");
+}