Please address the comments from this code review:

## Overall Comments
- The `system_prompt` string literals in `_handle_conversation_title` are implicitly concatenated and currently result in `"core topic.If the input"` (missing space after `core topic.`); add a trailing space or separate sentence to avoid this typo in the prompt sent to the LLM.
- Consider extracting the conversation-title generation prompt into a shared helper or constant used by both `_handle_webchat` and `_handle_conversation_title` so that future changes to the title-generation logic remain consistent across platforms.
- Since `_handle_conversation_title` is launched via `asyncio.create_task`, it may be worth wrapping the whole function body in a broad try/except or adding a done-callback to log unexpected exceptions from `conv_mgr` calls so they don’t become unobserved background task errors.

## Individual Comments

### Comment 1
<location path="astrbot/core/astr_main_agent.py" line_range="850-855" />
<code_context>
+        return
+
+    # 获取会话对象，检查是否已有标题
+    conversation = await conv_mgr.get_conversation(umo, cid)
+    if not conversation or not user_prompt:
+        return
+
+    # 如果已有标题，跳过生成
+    if conversation.title:
+        return
+
</code_context>
<issue_to_address>
**issue (bug_risk):** There may be a race condition if multiple title-generation tasks run concurrently for the same conversation.

Since `_handle_conversation_title` is spawned via `asyncio.create_task` and only checks `conversation.title` once, two concurrent requests for the same `umo/cid` can both see an empty title, generate different titles, and race to update it. To make this idempotent, either re-check the title (or re-fetch the conversation) immediately before `update_conversation`, or use a conditional update that only sets the title if it is still empty.
</issue_to_address>

### Comment 2
<location path="astrbot/core/astr_main_agent.py" line_range="878-889" />
<code_context>
+
+    if llm_resp and llm_resp.completion_text:
+        title = llm_resp.completion_text.strip()
+        if not title or "<None>" in title:
+            return
+        logger.info(
</code_context>
<issue_to_address>
**suggestion (bug_risk):** Using a substring check for "<None>" might filter out legitimate titles.

This condition rejects any title containing "<None>", which could exclude valid titles. Consider normalizing the string (e.g., strip whitespace, normalize case) and then doing an exact comparison, e.g. `title == "<None>"` (and maybe a lowercase variant), instead of a substring check.

```suggestion
    if llm_resp and llm_resp.completion_text:
        title = llm_resp.completion_text.strip()
        # Normalize title for comparison to avoid filtering out legitimate titles
        normalized_title = title.strip().lower()
        if not title or normalized_title in ("<none>", "none"):
            return
        logger.info(
            "Generated conversation title for %s: %s", umo, title
        )
        await conv_mgr.update_conversation(
            unified_msg_origin=umo,
            conversation_id=cid,
            title=title,
        )
```
</issue_to_address>