feat: enable Watchtower HTTP API and use internal registry

- Add HTTP API to Watchtower for CI/CD triggered updates
- Update custom container images to use git.schweitz.internal
- Add GITEA_TOKEN env var to scheduler for release cleanup task

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

stacks/core-api.yml

@@ -5,11 +5,11 @@ version: '3.8'
 # Port: 8083 (HTTP API)
 # Network: docker-dataplane (shared infrastructure network)
 #
-# Container image built from: tower-of-joy:3002/jpmschweitzer/core-api (internal registry)
+# Container image built from: git.schweitz.internal/jpmschweitzer/core-api (internal registry)
 
 services:
   core-api:
-    image: tower-of-joy:3002/jpmschweitzer/core-api:latest
+    image: git.schweitz.internal/jpmschweitzer/core-api:latest
     container_name: core-api
     restart: unless-stopped