feat: interactive inline buttons, SMTP reply, AI reply suggestions

- Inline keyboard: view original / back to summary toggle per message
- SMTP config per account for sending replies
- Reply button: click, type message, auto-send via SMTP
- AI Reply button: generates 3 suggestions via DeepSeek
  - Simple replies (OK, Got it) send immediately on tap
  - Substantive replies require confirm before send
  - Hides AI Reply button when AI determines reply unnecessary
- Telegram long polling integrated into main loop for real-time interaction

src/smtp_client.py

@@ -0,0 +1,32 @@
+import smtplib
+from email.mime.text import MIMEText
+from email.mime.multipart import MIMEMultipart
+from src.config import EmailAccount
+from src.retry import retry
+
+
+@retry()
+def send_reply(account: EmailAccount, to_addr: str, subject: str, body: str):
+    if not account.smtp:
+        raise RuntimeError(f"账号 {account.username} 未配置 SMTP")
+
+    s = account.smtp
+    if s.use_ssl:
+        conn = smtplib.SMTP_SSL(s.server, s.port, timeout=15)
+    else:
+        conn = smtplib.SMTP(s.server, s.port, timeout=15)
+        if s.use_starttls:
+            conn.starttls()
+
+    conn.login(account.username, account.password)
+
+    reply_subject = subject if subject.lower().startswith("re:") else f"Re: {subject}"
+
+    msg = MIMEMultipart("alternative")
+    msg["From"] = account.username
+    msg["To"] = to_addr
+    msg["Subject"] = reply_subject
+    msg.attach(MIMEText(body, "plain", "utf-8"))
+
+    conn.sendmail(account.username, [to_addr], msg.as_string())
+    conn.quit()