refactor: extract core-api to standalone repository

Core-API service moved to git.schweitz.net/jpmschweitzer/core-api
- Source code removed from this repository
- Stack file updated to use container image from Gitea registry
- Documentation updated with external service reference
- Removed obsolete docs/services/core-api.md (docs now in core-api repo)

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

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

README.md

@@ -30,8 +30,8 @@
 - [NPM Logging Guide](docs/guides/npm-logging-guide.md) - Nginx Proxy Manager logging
 
 #### Services
-- [Core API](docs/services/core-api.md) - Infrastructure management and AI orchestration
 - [Organizr Widgets](docs/services/organizr-widgets.md) - Service control dashboard
+- [External Services](docs/EXTERNAL_SERVICES.md) - Services in separate repositories
 
 #### Reference
 - [Stacks Reference](docs/reference/stacks.md) - All Docker Compose stacks
@@ -145,8 +145,7 @@ deactivate
 
 ### Service Development
 
-See individual service documentation:
-- [Core API Development](docs/services/core-api.md#development)
+See [External Services](docs/EXTERNAL_SERVICES.md) for services maintained in separate repositories.
 
 ## Service Ports Reference