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/routers/health.py

@@ -128,6 +128,26 @@ async def health_check(
             ComponentHealth(name="fail2ban", healthy=False, message="Socket not reachable"),
         )
 
+    # --- External logging check ---
+    external_log_state: Literal["ok", "error", "disabled", "unknown"] = "unknown"
+    effective_settings: Settings = (
+        app_state.runtime_settings if app_state.runtime_settings is not None else app_state.settings
+    )
+    try:
+        ext_log_failed = getattr(app_state.runtime_state, "external_log_init_failed", False)
+        if effective_settings.external_logging_enabled and effective_settings.external_logging_provider:
+            if ext_log_failed:
+                external_log_state = "error"
+                components.append(
+                    ComponentHealth(name="external_logging", healthy=False, message="Handler initialization failed"),
+                )
+            else:
+                external_log_state = "ok"
+        else:
+            external_log_state = "disabled"
+    except AttributeError:  # pragma: no cover - defensive
+        external_log_state = "unknown"
+
     # --- Overall status ---
     overall_status: Literal["ok", "degraded", "unavailable"]
     if not fail2ban_online:
@@ -148,6 +168,7 @@ async def health_check(
             database="ok" if db_healthy else "error",
             scheduler=scheduler_state,
             cache=cache_state,
+            external_logging=external_log_state,
             components=components,
         ).model_dump(),
     )