feat: add Grafana Faro RUM, fix dashboards, add Grafana to admin nav

- Add @grafana/faro-web-sdk to UI; wire initializeFaro in hooks.client.ts
  gated on PUBLIC_FARO_COLLECTOR_URL (no-op in dev)
- Add Grafana Alloy service (faro.receiver) to homelab compose;
  Faro endpoint → alloy:12347 (faro.libnovel.cc via cloudflared)
- Add PUBLIC_FARO_COLLECTOR_URL env var to docker-compose.yml UI service
- Add Web Vitals dashboard (web-vitals.json): LCP/INP/CLS/TTFB/FCP p75
  stats + LCP/TTFB time-series + Faro exception logs from Loki
- Fix runner.json: strip libnovel_ prefix from all metric names
- Fix backend.json: replace 5 dead http_client_* panels with
  spanmetrics-based equivalents (Request Rate by Span Name + Latency
  by Span Name p95)
- Fix OTel collector: add service.telemetry.metrics.address: 0.0.0.0:8888
  so Prometheus can scrape collector self-metrics
- Add Grafana link to admin nav external tools; add admin_nav_grafana
  message key to all 5 locale files; recompile paraglide

homelab/docker-compose.yml

@@ -18,6 +18,7 @@
 #   uptime.libnovel.cc    → uptime-kuma:3001
 #   push.libnovel.cc      → gotify:80
 #   grafana.libnovel.cc   → grafana:3000
+#   faro.libnovel.cc      → alloy:12347
 
 services:
 
@@ -346,6 +347,23 @@ services:
       timeout: 5s
       retries: 5
 
+  # ── Grafana Alloy (Faro RUM receiver) ───────────────────────────────────────
+  # Receives browser telemetry from @grafana/faro-web-sdk (Web Vitals, traces,
+  # errors). Exposes POST /collect at faro.libnovel.cc via cloudflared.
+  # Forwards traces to otel-collector (→ Tempo) and logs to Loki directly.
+  alloy:
+    image: grafana/alloy:latest
+    restart: unless-stopped
+    command: ["run", "--server.http.listen-addr=0.0.0.0:12348", "/etc/alloy/alloy.river"]
+    volumes:
+      - ./otel/alloy.river:/etc/alloy/alloy.river:ro
+    expose:
+      - "12347"  # Faro HTTP receiver (POST /collect)
+      - "12348"  # Alloy UI / health endpoint
+    depends_on:
+      - otel-collector
+      - loki
+
   # ── OTel Collector ──────────────────────────────────────────────────────────
   # Receives OTLP from backend/ui/runner, fans out to Tempo + Prometheus + Loki.
   otel-collector: