chore(deploy): rework k8s pipeline, monitoring and postgres 17

Deploy workflow uses git-tracked manifests, DISABLED flag and kustomize overlays; add webinar-checker metrics with ServiceMonitor and alerts; upgrade shared postgres to 17 with statuspage DB and probes/resources.

postgres/shared-compose.yaml

@@ -1,6 +1,6 @@
 services:
   postgres:
-    image: postgres:15.19-alpine
+    image: postgres:17.11-alpine
     container_name: homelab-postgres
     restart: unless-stopped
     env_file: