refactor: move credentials to .env and add python-dotenv support

Replace hardcoded database credentials, ntfy tokens, and Uptime Kuma
push URLs with environment variable lookups via python-dotenv.
Add .env.example template and update .gitignore to exclude .env.

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

config/__init__.py

@@ -1,6 +1,9 @@
 # config/__init__.py
 # 统一配置导出接口
 
+from dotenv import load_dotenv
+load_dotenv()
+
 # 数据库配置
 from .database import SQL_SERVER_CONFIG, SQL_SERVER_CONN, DB_CONFIG, ACCESS_DRIVER