refactor(backend): external logging metrics, required mode, health checks

- Add external_logging_init_failures counter
- Add external_log_required flag, raise if init fails and required
- Health endpoint: add external_logging status check
- Blocklist service: enrich with metadata fields, update import logic
- Health check task: add runtime_state dependency, fix return typing
- Metrics: add Histogram for request latencies
- Frontend: align BlocklistImportLogSection props
- Docs: update deployment guide, remove stale tasks

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/app/utils/runtime_state.py

@@ -125,6 +125,7 @@ class RuntimeState:
     last_activation: ActivationRecord | None = None
     runtime_settings: Settings | None = None
     jail_service_state: JailServiceState = field(default_factory=JailServiceState)
+    external_log_init_failed: bool = False
 
 
 class ApplicationState(State):