feat: show recipient & AI-generated subject in summary

- AI now generates a concise subject title (not copy original)
- AI prompt includes recipient field in JSON schema
- Telegram message shows recipient and uses AI-generated title

src/ai_client.py

@@ -8,7 +8,8 @@ SYSTEM_PROMPT = """你是一个邮件摘要助手。请分析邮件内容并以
 
 返回格式必须严格遵循以下 JSON schema：
 {
-  "subject": "邮件主题",
+  "subject": "你概括的简短标题（10字以内）",
+  "recipient": "收件邮箱地址",
   "sender": "发件人",
   "summary": "50字以内的核心摘要",
   "priority": "high/medium/low",
@@ -17,12 +18,13 @@ SYSTEM_PROMPT = """你是一个邮件摘要助手。请分析邮件内容并以
   "key_points": ["关键要点1", "关键要点2"]
 }
 
+其中 subject 字段不能照抄原邮件主题，必须是你总结生成的简短标题。
 只返回 JSON，不要包含任何其他文字。"""
 
 
 @retry()
-def summarize_email(ai_cfg: AIConfig, subject: str, sender: str, body: str) -> dict[str, Any]:
-    content = f"发件人: {sender}\n主题: {subject}\n正文:\n{body[:4000]}"
+def summarize_email(ai_cfg: AIConfig, recipient: str, subject: str, sender: str, body: str) -> dict[str, Any]:
+    content = f"收件人: {recipient}\n发件人: {sender}\n主题: {subject}\n正文:\n{body[:4000]}"
 
     payload = {
         "model": ai_cfg.model,