fix: Windows compatibility and startup scripts

- Add explicit .env loading in config.py for Windows compatibility
- Add backend directory to sys.path in main.py to fix module imports
- Add start.bat and start-full.bat for Windows startup
- Add frontend/package-lock.json for dependency tracking

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

backend/app/config.py

@@ -1,9 +1,17 @@
 import base64
+import os
 from pathlib import Path
 from typing import Optional
 from pydantic import field_validator
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
+# Load .env file explicitly - Windows compatibility
+# This ensures environment variables are loaded before Settings instantiation
+_env_path = Path(__file__).parent.parent.parent / '.env'
+if _env_path.exists():
+    from dotenv import load_dotenv
+    load_dotenv(_env_path, override=True)
+
 
 class Settings(BaseSettings):
     """应用配置，从环境变量加载."""