feat: add IM channels for Feishu, Slack, and Telegram (#1010)

* feat: add IM channels system for Feishu, Slack, and Telegram integration

Bridge external messaging platforms to DeerFlow via LangGraph Server with
async message bus, thread management, and per-channel configuration.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: address review comments on IM channels system

Fix topic_id handling in store remove/list_entries and manager commands,
correct Telegram reply threading, remove unused imports/variables, update
docstrings and docs to match implementation, and prevent config mutation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* update skill creator

* fix im reply text

* fix comments

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/agents/middlewares/memory_middleware.py

@@ -40,9 +40,7 @@ def _filter_messages_for_memory(messages: list[Any]) -> list[Any]:
     Returns:
         Filtered list containing only user inputs and final assistant responses.
     """
-    _UPLOAD_BLOCK_RE = re.compile(
-        r"<uploaded_files>[\s\S]*?</uploaded_files>\n*", re.IGNORECASE
-    )
+    _UPLOAD_BLOCK_RE = re.compile(r"<uploaded_files>[\s\S]*?</uploaded_files>\n*", re.IGNORECASE)
 
     filtered = []
     skip_next_ai = False
@@ -52,9 +50,7 @@ def _filter_messages_for_memory(messages: list[Any]) -> list[Any]:
         if msg_type == "human":
             content = getattr(msg, "content", "")
             if isinstance(content, list):
-                content = " ".join(
-                    p.get("text", "") for p in content if isinstance(p, dict)
-                )
+                content = " ".join(p.get("text", "") for p in content if isinstance(p, dict))
             content_str = str(content)
             if "<uploaded_files>" in content_str:
                 # Strip the ephemeral upload block; keep the user's real question.