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>

.gitignore

@@ -6,6 +6,9 @@ log
 *.spec
 temp
 
+# 环境变量
+.env
+
 # Claude 临时文件
 .claude/
 tmpclaude-*