fix(feishu): remove resuming to avoid 10-min streaming card timeout

Feishu streaming cards auto-close after 10 minutes from creation,
regardless of update activity. With resuming enabled, a single card
lives across multiple tool-call rounds and can exceed this limit,
causing the final response to be silently lost.

Remove the _resuming logic from send_delta so each tool-call round
gets its own short-lived streaming card (well under 10 min). Add a
fallback that sends a regular interactive card when the final
streaming update fails.

docs/CHANNEL_PLUGIN_GUIDE.md

@@ -290,7 +290,6 @@ async def send_delta(self, chat_id: str, delta: str, metadata: dict[str, Any] |
 |------|---------|
 | `_stream_delta: True` | A content chunk (delta contains the new text) |
 | `_stream_end: True` | Streaming finished (delta is empty) |
-| `_resuming: True` | More streaming rounds coming (e.g. tool call then another response) |
 
 ### Example: Webhook with Streaming