refactor: remove unused web UI port configuration

The web UI (docs/index.html, portfolio.html) exists but is not served
in API mode. Removing the port configuration to eliminate confusion.

Changes:
- Remove port 8888 mapping from docker-compose.yml
- Remove WEB_HTTP_PORT from .env.example
- Update Dockerfile EXPOSE to only port 8080
- Update CHANGELOG.md to document removal

Technical details:
- Web UI static files remain in docs/ folder (legacy from batch mode)
- These were designed for JSONL file format, not the new SQLite database
- No web server was ever started in entrypoint.sh for API mode
- Port 8888 was exposed but nothing listened on it

Result:
- Cleaner configuration (1 fewer port mapping)
- Only REST API (8080) is exposed
- Eliminates user confusion about non-functional web UI

Dockerfile

@@ -33,8 +33,8 @@ RUN mkdir -p data logs data/agent_data
 # Make entrypoint executable
 RUN chmod +x entrypoint.sh
 
-# Expose MCP service ports, API server, and web dashboard
-EXPOSE 8000 8001 8002 8003 8080 8888
+# Expose API server port (MCP services are internal only)
+EXPOSE 8080
 
 # Set Python to run unbuffered for real-time logs
 ENV PYTHONUNBUFFERED=1