fix(feishu): prevent tool hint stacking and clean hints on stream_end

Three fixes for inline tool hints:

1. Consecutive tool hints now replace the previous one instead of
   stacking — the old suffix is stripped before appending the new one.

2. When _resuming flushes the buffer, any trailing tool hint suffix
   is removed so it doesn't persist into the next streaming segment.

3. When final _stream_end closes the card, tool hint suffix is
   cleaned from the text before the final card update.

Adds 3 regression tests covering all three scenarios.

Made-with: Cursor

nanobot/channels/feishu.py

@@ -1287,6 +1287,9 @@ class FeishuChannel(BaseChannel):
                 # next segment appends to the same card.
                 buf = self._stream_bufs.get(chat_id)
                 if buf and buf.card_id and buf.text:
+                    if buf.tool_hint_len > 0:
+                        buf.text = buf.text[:-buf.tool_hint_len]
+                        buf.tool_hint_len = 0
                     buf.sequence += 1
                     await loop.run_in_executor(
                         None, self._stream_update_text_sync, buf.card_id, buf.text, buf.sequence,
@@ -1296,6 +1299,9 @@ class FeishuChannel(BaseChannel):
             buf = self._stream_bufs.pop(chat_id, None)
             if not buf or not buf.text:
                 return
+            if buf.tool_hint_len > 0:
+                buf.text = buf.text[:-buf.tool_hint_len]
+                buf.tool_hint_len = 0
             if buf.card_id:
                 buf.sequence += 1
                 await loop.run_in_executor(
@@ -1376,6 +1382,8 @@ class FeishuChannel(BaseChannel):
                     return
                 buf = self._stream_bufs.get(msg.chat_id)
                 if buf and buf.card_id:
+                    if buf.tool_hint_len > 0:
+                        buf.text = buf.text[:-buf.tool_hint_len]
                     suffix = f"\n\n---\n🔧 {hint}"
                     buf.text += suffix
                     buf.tool_hint_len = len(suffix)