Windows 兼容性修复 + Dify API 适配 + 企微 WS 加载优化 (#2470)

* fix: Windows fsync requires write access to file descriptor

- _fsync_file: os.O_RDONLY -> os.O_RDWR (Windows _commit() requires write access)
- _fsync_directory: tolerate OSError on fsync and os.open (chmod 0o700 blocks access on Windows)

* fix: Dify SSE empty data lines and upload response format mismatch

- Skip malformed/flushed SSE data lines (JSONDecodeError)
- Accept HTTP 200 besides 201 for file upload response
- Unwrap data wrapper in upload response (resp.get('data', resp))

* feat: WeCom WS mode sends empty initial stream frame for loading spinner

Send an empty reply_stream frame immediately after stream session
creation so the WeCom client shows its built-in loading indicator
while the pipeline processes the message (e.g. RAG retrieval).

* fix(compat): harden Windows, Dify, and WeCom changes

* fix(migration): clean interrupted SQLite temp files

---------

Co-authored-by: Hyu <chenhyu@proton.me>

src/langbot/libs/wecom_ai_bot_api/ws_client.py

@@ -936,6 +936,13 @@ class WecomBotWsClient:
                     'chat_type': message_data.get('type', 'single'),
                 }
                 self._prune_stream_state()
+                # Send an initial empty stream frame so the WeCom client
+                # shows its built-in loading spinner while the pipeline
+                # processes the message (e.g. RAG retrieval).
+                try:
+                    await self.reply_stream(req_id, stream_id, '', finish=False)
+                except Exception:
+                    await self.logger.warning(f'Failed to send initial stream frame: {traceback.format_exc()}')
             message_data['stream_id'] = stream_id
             message_data['req_id'] = req_id