feat: init AI email summarization bot

- Multi-account IMAP email polling with UID tracking
- DeepSeek API integration with JSON Mode structured output
- Telegram notification with formatted MarkdownV2 message
- YAML config with dataclass-based type validation
- Graceful shutdown on SIGINT/SIGTERM
- 60s default polling interval

config.yaml.example

@@ -0,0 +1,22 @@
+email_accounts:
+  - imap_server: "imap.gmail.com"
+    imap_port: 993
+    username: "your_email@gmail.com"
+    password: "your_app_password"
+
+  - imap_server: "imap.qq.com"
+    imap_port: 993
+    username: "your_email@qq.com"
+    password: "your_authorization_code"
+
+ai:
+  api_key: "sk-your_deepseek_api_key"
+  model: "deepseek-chat"
+  base_url: "https://api.deepseek.com"
+
+telegram:
+  bot_token: "1234567890:ABCdefGHIjklmNOPqrstUVwxyz"
+  chat_id: "123456789"
+
+polling:
+  interval_seconds: 60