feat: add /sentry-debug endpoint for verification

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

backend/app/main.py

@@ -252,6 +252,12 @@ async def health_check():
     return {"status": "healthy"}
 
 
+@app.get("/sentry-debug")
+async def trigger_error():
+    """Sentry verification endpoint — triggers a test error."""
+    division_by_zero = 1 / 0
+
+
 if settings.DEBUG:
     @app.get("/debug/cors")
     async def debug_cors():