feat(deploy): add WebRTC Prometheus alert rules

deploy/truenas/core/prom/rules/webrtc-alerts.yml

@@ -0,0 +1,45 @@
+groups:
+  - name: dragonfork-webrtc
+    rules:
+      - alert: WebRTCWHEPErrorRateHigh
+        expr: |
+          sum by (stream_id) (
+            rate(dragonfork_webrtc_whep_requests_total{code=~"4..|5.."}[5m])
+          ) > 0.5
+        for: 5m
+        labels:
+          severity: warning
+        annotations:
+          summary: "WHEP error rate high on stream {{ $labels.stream_id }}"
+          description: "Sustained 4xx/5xx rate >0.5/sec for 5m."
+
+      - alert: WebRTCICEEstablishmentSlow
+        expr: |
+          histogram_quantile(0.95,
+            sum by (le, stream_id) (
+              rate(dragonfork_webrtc_ice_establishment_duration_seconds_bucket[10m])
+            )
+          ) > 3
+        for: 10m
+        labels:
+          severity: warning
+        annotations:
+          summary: "ICE establishment p95 >3s on {{ $labels.stream_id }}"
+
+      - alert: WebRTCICEFailureRateHigh
+        expr: |
+          sum by (stream_id) (rate(dragonfork_webrtc_ice_failures_total[5m])) > 0.2
+        for: 5m
+        labels:
+          severity: warning
+        annotations:
+          summary: "ICE failures sustained on {{ $labels.stream_id }}"
+
+      - alert: WebRTCFFmpegLegFailure
+        expr: |
+          increase(dragonfork_webrtc_ffmpeg_leg_failures_total[5m]) > 0
+        labels:
+          severity: critical
+        annotations:
+          summary: "FFmpeg RTP leg failed on {{ $labels.stream_id }} ({{ $labels.leg }})"
+          description: "Process stopped while peers were active. Check FFmpeg logs."