fix: let assembly defects pierce the gate wrappers

Independent verification caught that the split shipped in the previous
commit did not actually hold on the only path production uses. The gate
wrappers re-raise GovernanceBackendError but nothing else, so
SourceNotConfiguredError fell into the following `except Exception` and
came back out as a governance_backend_down failure with retry_after_s=5.0.
A misconfigured source name would still retry forever and never surface.

The existing tests missed it because both of them call the private _cfg()
directly, one layer below the wrapper the governance loops actually go
through. The regression test goes through QuotaGate.

telemetry.py has to widen its terminal catch in the same commit: once the
wrapper stops relabeling the error, it is no longer a GovernanceBackendError,
and it is raised before any attempt exists, so the path would have recorded
no telemetry at all.

Also corrects the leak path count from three to five. QuotaGate.stats and
BreakerGate.retry_after_s are not wrapped by _record_quietly either.

src/polygateway/middleware/telemetry.py

@@ -17,7 +17,11 @@ from typing import TYPE_CHECKING
 
 from loguru import logger
 
-from polygateway.errors import GatewayUnavailableError, GovernanceBackendError
+from polygateway.errors import (
+    GatewayUnavailableError,
+    GovernanceBackendError,
+    SourceNotConfiguredError,
+)
 from polygateway.middleware.cache import digest_messages
 from polygateway.types import canonical_sampling_json, merge_sampling
 
@@ -247,7 +251,7 @@ class TelemetryMW:
         started = self._now()
         try:
             response = await call_next(request)
-        except (GatewayUnavailableError, GovernanceBackendError) as exc:
+        except (GatewayUnavailableError, GovernanceBackendError, SourceNotConfiguredError) as exc:
             await self._emitter.emit_terminal_failure(
                 request=request,
                 call_id=str(uuid.uuid4()),