[ci skip] Fix all active Prometheus alerts

- meshcentral: rename port from "https" to "http" — MeshCentral serves
  plain HTTP when REVERSE_PROXY=true, but Traefik inferred HTTPS from the
  port name, causing 100% 5xx errors
- osm-routing/otp: scale to 0 — TfL GTFS data expired, OTP crash-loops
  trying to build graph with no valid transit trips
- wireguard: add prometheus.io/port=9586 annotation — without it,
  Prometheus tried scraping all container ports (51820 UDP, 80)
- travel-blog: remove stale prometheus.io annotations and dead port 9113
  — nginx-exporter sidecar was commented out but annotations remained
- dawarich: remove prometheus.io annotations — exporter env vars are
  commented out so nothing listens on port 9394
- monitoring: raise CPU temp threshold 60°C→75°C (E5-2699 v4 Tcase is
  79°C), lower registry cache threshold 50%→25%, add minimum traffic
  floor (>0.1 req/s) to 4xx/5xx rate alerts to prevent false positives
  on low-traffic services

modules/kubernetes/wireguard/main.tf

@@ -84,6 +84,7 @@ resource "kubernetes_deployment" "wireguard" {
         }
         annotations = {
           "prometheus.io/scrape" = "true"
+          "prometheus.io/port"   = "9586"
         }
       }
       spec {