feat(gateway): Docker Gateway 봇 + HTTP API 구현 #task-311

- gateway.py: Collector↔Gateway HTTP API (pending, response, chat, register, commands)
- Dockerfile + docker-compose.yml: BOT_MODE=gateway, port 8585
- main.py: gateway 모드 (watcher 비활성, GatewayAPI 시작)
- config.py: gateway 모드 BRAIN_PATH 검증 스킵
- requirements.txt: aiohttp 추가
- docs/usage-guide.md: Docker 배포 섹션 추가
- Extension VSIX v0.3.9 빌드 (auto-approve 포함)

Dockerfile

@@ -0,0 +1,19 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+# Install dependencies
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt aiohttp>=3.9.0
+
+# Copy application code
+COPY config.py bridge.py bot.py watcher.py gateway.py main.py ./
+COPY .env* ./
+
+# Default environment (can be overridden via docker-compose)
+ENV BOT_MODE=gateway
+ENV GATEWAY_PORT=8585
+
+EXPOSE 8585
+
+CMD ["python", "main.py"]