🔧 Fix CORS and API endpoint issues

- Fix API endpoint paths (remove trailing slashes for 405 errors)
- Update API URLs to use api-todo.hyungi.net subdomain for HTTPS compatibility
- Improve CORS settings parsing in backend (handle brackets and quotes)
- Add frontend volume mount to docker-compose for real-time file updates
- Update Synology deployment config with wildcard CORS settings

Resolves:
- 405 Method Not Allowed errors
- Mixed Content security issues (HTTPS → HTTP)
- CORS preflight request failures
- Docker build requirements for every file change

Tested: API endpoints now correctly use HTTPS subdomain, eliminating security blocks

backend/src/main.py

@@ -39,7 +39,9 @@ cors_origins = []
 if settings.CORS_ORIGINS == "*":
     cors_origins = ["*"]
 else:
-    cors_origins = [origin.strip() for origin in settings.CORS_ORIGINS.split(",")]
+    # 공백과 대괄호 제거 후 쉼표로 분리
+    cors_str = settings.CORS_ORIGINS.strip('[]"\'')
+    cors_origins = [origin.strip().strip('"\'') for origin in cors_str.split(",") if origin.strip()]
 
 logger.info(f"🌐 CORS Origins: {cors_origins}")