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

.env.example

@@ -21,10 +21,6 @@ JINA_API_KEY=your_jina_key_here # https://jina.ai/
 # Used for Windmill integration and external API access
 API_PORT=8080
 
-# Web Interface Host Port (exposed on host machine)
-# Container always uses 8888 internally
-WEB_HTTP_PORT=8888
-
 # Agent Configuration
 AGENT_MAX_STEP=30