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/summarizer.py

@@ -29,7 +29,8 @@ def _process_account(cfg: Config, acct):
     for mail in emails:
         try:
             logger.info(f"  正在摘要: {mail.subject}")
-            summary = summarize_email(cfg.ai, mail.subject, mail.sender, mail.body)
+            summary = summarize_email(cfg.ai, acct.username, mail.subject, mail.sender, mail.body)
+            summary["recipient"] = acct.username
             text = format_summary(summary)
             send_message(cfg.telegram, text)
             seen_uids.append(mail.uid)