feat: cancel button, regenerate AI replies, custom reply hints

- Reply prompt now has an inline '取消回复' button instead of typing text
- AI reply selection adds '换一批' button: passes all previous suggestions
  to AI to generate different replies
- '我想说：' button: lets user type a hint/tone instruction, AI tailors
  suggestions accordingly
- Cancel button also works on prompt/hint messages (deletes them)
- Extract _show_ai_suggestions helper for reuse

src/ai_client.py

@@ -49,6 +49,43 @@ def summarize_email(ai_cfg: AIConfig, recipient: str, subject: str, sender: str,
     return _call_deepseek(ai_cfg, payload)
 
 
+MORE_REPLIES_PROMPT = """你是一个邮件回复助手。根据以下邮件内容生成3个完全不同的建议回复。
+
+以下是一些已经生成过的回复，请生成全新的回复，不要与已有回复重复。
+
+返回 JSON:
+{
+  "suggestions": [
+    {"text": "回复内容"},
+    {"text": "回复内容"},
+    {"text": "回复内容"}
+  ]
+}
+每条回复控制在 50 字以内。
+只返回 JSON，不要包含任何其他文字。"""
+
+
+@retry()
+def generate_more_replies(ai_cfg: AIConfig, sender: str, subject: str, body: str,
+                          previous_suggestions: list[dict], user_hint: str = "") -> list[dict]:
+    content = f"发件人: {sender}\n主题: {subject}\n正文:\n{body[:4000]}\n\n已生成过的回复:\n"
+    for i, s in enumerate(previous_suggestions, 1):
+        content += f"{i}. {s['text']}\n"
+    if user_hint:
+        content += f"\n用户要求: {user_hint}"
+
+    payload = {
+        "model": ai_cfg.model,
+        "messages": [
+            {"role": "system", "content": MORE_REPLIES_PROMPT},
+            {"role": "user", "content": content},
+        ],
+        "response_format": {"type": "json_object"},
+    }
+    result = _call_deepseek(ai_cfg, payload)
+    return result.get("suggestions", [])
+
+
 def _call_deepseek(ai_cfg: AIConfig, payload: dict) -> dict:
     headers = {
         "Authorization": f"Bearer {ai_cfg.api_key}",