ci(main): trigger image builds on main branch commits

.gitea/workflows/build-prod.yaml

@@ -1,13 +1,13 @@
-# Build and push on prod branch — triggered automatically when commits land on prod.
+# Build and push on main branch — triggered automatically when commits land on main.
 # Tag is commit short SHA: unique, immutable, maps to exactly one commit.
 # Image: forgejo.riotpiao.com/rock/api-gateway:<commit-sha>
 #
-# No write-back, no git push — ArgoCD Image Updater or manual deployment pulls new builds.
-name: Build (prod)
+# ArgoCD auto-deploys to api namespace as revisions roll in.
+name: Build and push
 
 on:
   push:
-    branches: [prod]
+    branches: [main]
 
 env:
   REGISTRY: forgejo.riotpiao.com