Phase 26: P1 architecture refactor — DI container, service layer, async callbacks

- config.py: APIConfig + AppConfig dataclasses, env vars centralized
- api_client.py: APIClientProtocol (Protocol) + HTTPAPIClient class, remove module-level globals
- services.py: ChatService, DocumentService, TTSService (TTS moved from app.py)
- container.py: manual DI container with lazy singleton properties
- app.py: all callbacks converted to async, asyncio.run() fully removed, container wired in
- .env.example: add TTS_EDGE_VOICE entry
- ROADMAP.md: P0/P1 checklist updated to reflect completed work

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,10 @@
+# 율봇 API 서버 주소
+YOULBOT_API_URL=http://localhost:8000
+
+# API 토큰 (youlbot/.env의 API_TOKEN과 동일하게 설정. 빈 값이면 개발 모드)
+YOULBOT_API_TOKEN=youlbot-ai-token!!@@1234
+
+# 음성 설정 (로컬 실행)
+WHISPER_MODEL_SIZE=small
+TTS_VOICE=Yuna
+TTS_EDGE_VOICE=ko-KR-SunHiNeural