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>

backend/app/api/deps.py

@@ -4,6 +4,7 @@ from fastapi import Depends, HTTPException, Request, status
 from fastapi.security import OAuth2PasswordBearer
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy import select
+import sentry_sdk
 
 from app.core.database import get_db
 from app.core.security import decode_token
@@ -92,6 +93,9 @@ async def get_current_active_user(
                 detail="password_change_required"
             )
 
+    # Set Sentry user context for error attribution
+    sentry_sdk.set_user({"id": str(current_user.id), "email": current_user.email})
+
     # Lightweight trial expiry check
     if current_user.account_id:
         from app.models.subscription import Subscription