argocd: add homelab-gateway application

Adds the homelab-gateway Argo CD Application pointing at
arcodange/homelab-gateway (user space, like dance-lessons-coach).

Image Updater watches gitea.arcodange.lab/arcodange/homelab-gateway:latest
with digest strategy.

Phase 1 of the Telegram webhook gateway — a long-running pod that
receives webhooks (no more polling) and routes per-bot to handler
implementations. Initial bot: @arcodange_factory_bot, slug=factory,
echo handler.

argocd/values.yaml

@@ -14,6 +14,11 @@ gitea_applications:
     annotations:
       argocd-image-updater.argoproj.io/image-list: webapp=gitea.arcodange.lab/arcodange-org/webapp:latest
       argocd-image-updater.argoproj.io/webapp.update-strategy: digest
+  homelab-gateway:
+    org: arcodange
+    annotations:
+      argocd-image-updater.argoproj.io/image-list: homelab-gateway=gitea.arcodange.lab/arcodange/homelab-gateway:latest
+      argocd-image-updater.argoproj.io/homelab-gateway.update-strategy: digest
   erp:
     annotations: {}
   cms: