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/channels/message_bus.py

@@ -0,0 +1,150 @@
+"""MessageBus — async pub/sub hub that decouples channels from the agent dispatcher."""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+import time
+from collections.abc import Callable, Coroutine
+from dataclasses import dataclass, field
+from enum import StrEnum
+from typing import Any
+
+logger = logging.getLogger(__name__)
+
+
+# ---------------------------------------------------------------------------
+# Message types
+# ---------------------------------------------------------------------------
+
+
+class InboundMessageType(StrEnum):
+    """Types of messages arriving from IM channels."""
+
+    CHAT = "chat"
+    COMMAND = "command"
+
+
+@dataclass
+class InboundMessage:
+    """A message arriving from an IM channel toward the agent dispatcher.
+
+    Attributes:
+        channel_name: Name of the source channel (e.g. "feishu", "slack").
+        chat_id: Platform-specific chat/conversation identifier.
+        user_id: Platform-specific user identifier.
+        text: The message text.
+        msg_type: Whether this is a regular chat message or a command.
+        thread_ts: Optional platform thread identifier (for threaded replies).
+        topic_id: Conversation topic identifier used to map to a DeerFlow thread.
+            Messages sharing the same ``topic_id`` within a ``chat_id`` will
+            reuse the same DeerFlow thread.  When ``None``, each message
+            creates a new thread (one-shot Q&A).
+        files: Optional list of file attachments (platform-specific dicts).
+        metadata: Arbitrary extra data from the channel.
+        created_at: Unix timestamp when the message was created.
+    """
+
+    channel_name: str
+    chat_id: str
+    user_id: str
+    text: str
+    msg_type: InboundMessageType = InboundMessageType.CHAT
+    thread_ts: str | None = None
+    topic_id: str | None = None
+    files: list[dict[str, Any]] = field(default_factory=list)
+    metadata: dict[str, Any] = field(default_factory=dict)
+    created_at: float = field(default_factory=time.time)
+
+
+@dataclass
+class OutboundMessage:
+    """A message from the agent dispatcher back to a channel.
+
+    Attributes:
+        channel_name: Target channel name (used for routing).
+        chat_id: Target chat/conversation identifier.
+        thread_id: DeerFlow thread ID that produced this response.
+        text: The response text.
+        artifacts: List of artifact paths produced by the agent.
+        is_final: Whether this is the final message in the response stream.
+        thread_ts: Optional platform thread identifier for threaded replies.
+        metadata: Arbitrary extra data.
+        created_at: Unix timestamp.
+    """
+
+    channel_name: str
+    chat_id: str
+    thread_id: str
+    text: str
+    artifacts: list[str] = field(default_factory=list)
+    is_final: bool = True
+    thread_ts: str | None = None
+    metadata: dict[str, Any] = field(default_factory=dict)
+    created_at: float = field(default_factory=time.time)
+
+
+# ---------------------------------------------------------------------------
+# MessageBus
+# ---------------------------------------------------------------------------
+
+OutboundCallback = Callable[[OutboundMessage], Coroutine[Any, Any, None]]
+
+
+class MessageBus:
+    """Async pub/sub hub connecting channels and the agent dispatcher.
+
+    Channels publish inbound messages; the dispatcher consumes them.
+    The dispatcher publishes outbound messages; channels receive them
+    via registered callbacks.
+    """
+
+    def __init__(self) -> None:
+        self._inbound_queue: asyncio.Queue[InboundMessage] = asyncio.Queue()
+        self._outbound_listeners: list[OutboundCallback] = []
+
+    # -- inbound -----------------------------------------------------------
+
+    async def publish_inbound(self, msg: InboundMessage) -> None:
+        """Enqueue an inbound message from a channel."""
+        await self._inbound_queue.put(msg)
+        logger.info(
+            "[Bus] inbound enqueued: channel=%s, chat_id=%s, type=%s, queue_size=%d",
+            msg.channel_name,
+            msg.chat_id,
+            msg.msg_type.value,
+            self._inbound_queue.qsize(),
+        )
+
+    async def get_inbound(self) -> InboundMessage:
+        """Block until the next inbound message is available."""
+        return await self._inbound_queue.get()
+
+    @property
+    def inbound_queue(self) -> asyncio.Queue[InboundMessage]:
+        return self._inbound_queue
+
+    # -- outbound ----------------------------------------------------------
+
+    def subscribe_outbound(self, callback: OutboundCallback) -> None:
+        """Register an async callback for outbound messages."""
+        self._outbound_listeners.append(callback)
+
+    def unsubscribe_outbound(self, callback: OutboundCallback) -> None:
+        """Remove a previously registered outbound callback."""
+        self._outbound_listeners = [cb for cb in self._outbound_listeners if cb is not callback]
+
+    async def publish_outbound(self, msg: OutboundMessage) -> None:
+        """Dispatch an outbound message to all registered listeners."""
+        logger.info(
+            "[Bus] outbound dispatching: channel=%s, chat_id=%s, listeners=%d, text_len=%d",
+            msg.channel_name,
+            msg.chat_id,
+            len(self._outbound_listeners),
+            len(msg.text),
+        )
+        for callback in self._outbound_listeners:
+            try:
+                await callback(msg)
+            except Exception:
+                logger.exception("Error in outbound callback for channel=%s", msg.channel_name)