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

docker-compose.yml

@@ -302,6 +302,8 @@ services:
       PUBLIC_UMAMI_SCRIPT_URL: "${PUBLIC_UMAMI_SCRIPT_URL}"
       # GlitchTip client + server-side error tracking
       PUBLIC_GLITCHTIP_DSN: "${PUBLIC_GLITCHTIP_DSN}"
+      # Grafana Faro RUM (browser Web Vitals, traces, errors)
+      PUBLIC_FARO_COLLECTOR_URL: "${PUBLIC_FARO_COLLECTOR_URL}"
       # OpenTelemetry tracing
       OTEL_EXPORTER_OTLP_ENDPOINT: "${OTEL_EXPORTER_OTLP_ENDPOINT}"
       OTEL_SERVICE_NAME: "ui"