software/openwebui: add OpenWebUI software release

Summary

• Add SlapOS software release for OpenWebUI (open-source AI chat interface)
• Python eggs via zc.recipe.egg with ~150 version pins
• HAProxy TLS frontend with WebSocket support
• Milvus vector DB backend (chromadb requires FTS5 not available in SlapOS Python)
• Google namespace package fix for pkg_resources compatibility
• JSON Schema parameter validation, monitor stack, logrotate, promises
• Configurable: port, ollama-url, openai-api-base-url, openai-api-key, webui-auth, log-level

Test plan

• Software release builds successfully
• Instance deploys and publishes connection parameters (url, frontend-url)
• OpenWebUI health endpoint responds
• Frontend accessible via published URL