feat(feishu): make reaction emoji configurable

Replace hardcoded THUMBSUP with configurable react_emoji field
in FeishuConfig, consistent with SlackConfig.react_emoji pattern.

Default remains THUMBSUP for backward compatibility.

nanobot/config/schema.py

@@ -42,6 +42,7 @@ class FeishuConfig(Base):
     encrypt_key: str = ""  # Encrypt Key for event subscription (optional)
     verification_token: str = ""  # Verification Token for event subscription (optional)
     allow_from: list[str] = Field(default_factory=list)  # Allowed user open_ids
+    react_emoji: str = "THUMBSUP"  # Emoji type for message reactions (e.g. THUMBSUP, OK, DONE, SMILE)
 
 
 class DingTalkConfig(Base):