fix: Circuit Breaker only triggers on transient DB errors, not HTTP exceptions

The CircuitBreakerMiddleware was blocking all requests (503 circuit_open) because
every exception in get_db() — including 401 Unauthorized, 403 Forbidden, 404 Not Found —
was calling record_failure() on the DB circuit breaker. This caused the circuit to
trip after 5 non-DB errors (e.g. failed login attempts during security testing).

Fix: Only call record_failure() when _is_transient_db_error(exc) returns True,
filtering out HTTP exceptions that are not DB-related.

app/core/db/__init__.py

@@ -224,7 +224,7 @@ async def get_db() -> AsyncGenerator[AsyncSession, None]:
     Used for normal API requests with tenant context set via RLS.
     Includes retry logic for transient connection errors.
     """
-    from app.core.resilience import get_circuit, retry_db
+    from app.core.resilience import get_circuit, retry_db, _is_transient_db_error
 
     async def _get_session():
         factory = get_session_factory()
@@ -235,9 +235,11 @@ async def get_db() -> AsyncGenerator[AsyncSession, None]:
         yield session
         await session.commit()
         await get_circuit("db").record_success()
-    except Exception:
+    except Exception as exc:
         await session.rollback()
-        await get_circuit("db").record_failure()
+        # Only record DB circuit failure for transient DB errors, not HTTP exceptions
+        if _is_transient_db_error(exc):
+            await get_circuit("db").record_failure()
         raise
     finally:
         await session.close()