feat(collector): RemoteTransport + CollectorBridge 구현 — Collector↔Gateway HTTP 통신 완성

- bridge.py RemoteTransport: HTTP 클라이언트, API Key auth, Gateway API 매핑
- collector.py CollectorBridge: 3개 async loop (pending 전달, response 폴링, commands 폴링)
- main.py: BOT_MODE=remote → CollectorBridge 실행 (Discord bot 없이)
- config.py: GATEWAY_API_KEY 설정
- .env.example: 모든 설정 항목 업데이트

.env.example

@@ -16,3 +16,13 @@ ACTIVE_TIMEOUT_SECONDS=300
 
 # Watcher Settings
 DEBOUNCE_SECONDS=2
+
+# Bot mode: 'local' (default, file-based) or 'gateway' (서버 Docker)
+BOT_MODE=local
+# Remote bridge URL (only used when BOT_MODE=remote)
+REMOTE_BRIDGE_URL=
+
+# Gateway API Key (보안)
+# 서버와 Collector에 동일한 키를 설정하세요
+# 생성: python -c "import secrets; print(secrets.token_urlsafe(32))"
+GATEWAY_API_KEY=