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/tasks/health_check.py

@@ -20,8 +20,10 @@ so that task logs can be correlated across runs.
 
 from __future__ import annotations
 
+import asyncio
 import datetime
 import uuid
+from contextvars import copy_context
 from typing import TYPE_CHECKING
 
 import structlog
@@ -69,20 +71,24 @@ async def _run_probe_with_resources(
 
     token = set_correlation_id(correlation_id)
     try:
-        await _do_probe_with_resources(settings, runtime_state)
+        # Use copy_context() so ContextVar values (e.g. correlation_id)
+        # propagate to any child asyncio tasks spawned inside the coroutine.
+        probe_task = asyncio.create_task(
+            _do_probe_with_resources(settings, runtime_state),
+            context=copy_context(),
+        )
+        await run_with_timeout("health_check", probe_task, HEALTH_PROBE_TIMEOUT_SECONDS)
     finally:
+        # Reset AFTER run_with_timeout completes, so child tasks still
+        # have the correlation ID in their context while they log.
         reset_correlation_id(token)
 
 
 async def _do_probe_with_resources(settings: Settings, runtime_state: RuntimeState) -> None:
     """Inner probe logic that runs with correlation context set."""
-
-    async def _do_probe() -> None:
-        socket_path: str = settings.fail2ban_socket
-        status: ServerStatus = await health_service.probe(socket_path)
-        process_health_probe_result(runtime_state, status)
-
-    await run_with_timeout("health_check", _do_probe(), HEALTH_PROBE_TIMEOUT_SECONDS)
+    socket_path: str = settings.fail2ban_socket
+    status: ServerStatus = await health_service.probe(socket_path)
+    process_health_probe_result(runtime_state, status)
 
 
 async def _run_probe(app: FastAPI) -> None: