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

docker-compose.yml

@@ -23,8 +23,6 @@ services:
     ports:
       # API server port (primary interface for external access)
       - "${API_PORT:-8080}:8080"
-      # Web dashboard
-      - "${WEB_HTTP_PORT:-8888}:8888"
     restart: unless-stopped  # Keep API server running
     healthcheck:
       test: ["CMD", "curl", "-f", "http://localhost:8080/health"]