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

ui/messages/id.json

@@ -471,5 +471,6 @@
   "feed_chapters_label": "{n} bab",
   "feed_browse_cta": "Jelajahi katalog",
   "feed_find_users_cta": "Temukan pembaca",
-  "admin_nav_gitea": "Gitea"
+  "admin_nav_gitea": "Gitea",
+  "admin_nav_grafana": "Grafana"
 }