fix: improve MCP service startup reliability

- Clarify OPENAI_API_BASE can be left empty for default endpoint
- Increase initial wait time from 3s to 5s
- Add health checking for all MCP services (ports 8000-8003)
- Retry up to 10 times with 1s intervals
- Install netcat for port checking
- Display warnings if services aren't ready

Helps diagnose and prevent MCP client initialization errors.

.env.example

@@ -5,7 +5,8 @@
 # Docker Compose automatically reads .env from project root
 
 # AI Model API Configuration
-OPENAI_API_BASE=https://your-openai-proxy.com/v1
+# OPENAI_API_BASE: Leave empty to use default OpenAI endpoint, or set to custom proxy URL
+OPENAI_API_BASE=
 OPENAI_API_KEY=your_openai_key_here # https://platform.openai.com/api-keys
 
 # Data Source Configuration