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/metrics.py

@@ -8,7 +8,15 @@ This module provides metrics collection for:
 
 from __future__ import annotations
 
-from prometheus_client import Counter, Gauge, Histogram, Summary, generate_latest, CollectorRegistry, CONTENT_TYPE_LATEST
+from prometheus_client import (
+    CONTENT_TYPE_LATEST,
+    CollectorRegistry,
+    Counter,
+    Gauge,
+    Histogram,
+    Summary,
+    generate_latest,
+)
 
 __all__ = [
     "get_metrics_registry",
@@ -19,6 +27,7 @@ __all__ = [
     "bans_total",
     "jails_total",
     "fail2ban_connection_errors",
+    "external_logging_init_failures",
 ]
 
 # Global registry
@@ -81,6 +90,12 @@ fail2ban_connection_errors = Counter(
     registry=get_metrics_registry(),
 )
 
+external_logging_init_failures = Counter(
+    "bangui_external_logging_init_failures_total",
+    "Total number of external logging handler initialization failures",
+    registry=get_metrics_registry(),
+)
+
 # Application startup and health
 
 app_uptime = Summary(

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):