feat(pii): export PII/audit events as a Prometheus counter (#10641)

The PII EventStore ring buffer is capacity-bound and meant for
recent-audit browsing via /api/pii/events; operators also want a
monotonic, scrape-friendly signal on /metrics — how many
detections/masks/blocks per hour, per origin, and whether the filter
stopped firing after a deploy (silent-failure class).

EventStore.Record is the single choke point every producer already goes
through (request middleware, response scrubbing, MITM proxy
connects/intercepts), so one lazily-initialised counter there covers all
paths without touching any producer:

  localai_pii_events_total{kind, origin, action, direction}

Same lazy otel.Meter pattern as core/services/routing/billing, so the
counter lands on the Prometheus-backed global MeterProvider installed by
the monitoring service. No behaviour change; label cardinality is
bounded (enum-like fields only, no pattern IDs or user IDs).

Assisted-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Signed-off-by: stefanwalcz <stefan.walcz@walcz.de>

core/services/routing/pii/metrics.go

@@ -0,0 +1,48 @@
+package pii
+
+import (
+	"context"
+	"sync"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/metric"
+)
+
+// Prometheus counter for PII events. The EventStore ring buffer is
+// capacity-bound and meant for recent-audit browsing; operators also want
+// a monotonic, scrape-friendly signal ("how many detections/blocks per
+// hour, did the filter stop firing after a deploy"). Record() is the
+// single choke point every producer already goes through (request
+// middleware, response scrubbing, MITM proxy connects/intercepts), so one
+// counter here covers all paths without touching the producers.
+//
+// Initialised lazily on first Record so the package works no matter when
+// (or whether) the Prometheus-backed global MeterProvider is installed —
+// same pattern as core/services/routing/billing.
+var (
+	metricsOnce   sync.Once
+	eventsCounter metric.Int64Counter
+)
+
+func recordEventMetric(e PIIEvent) {
+	metricsOnce.Do(func() {
+		meter := otel.Meter("github.com/mudler/LocalAI")
+		c, err := meter.Int64Counter(
+			"localai_pii_events_total",
+			metric.WithDescription("PII/audit events recorded, labeled by kind, origin, action and direction"),
+		)
+		if err == nil {
+			eventsCounter = c
+		}
+	})
+	if eventsCounter == nil {
+		return
+	}
+	eventsCounter.Add(context.Background(), 1, metric.WithAttributes(
+		attribute.String("kind", string(e.Kind)),
+		attribute.String("origin", string(e.Origin)),
+		attribute.String("action", string(e.Action)),
+		attribute.String("direction", string(e.Direction)),
+	))
+}

core/services/routing/pii/store.go

@@ -58,6 +58,7 @@ type memoryEventStore struct {
 }
 
 func (s *memoryEventStore) Record(_ context.Context, e PIIEvent) error {
+	recordEventMetric(e)
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	s.ring[s.cursor] = e