Fix webhook avatar mismatch: pass avatar_url at send time

- Fixed missing client parameter in animated GIF webhook update path
- Added get_persona_avatar_urls() helper that returns bot's current Discord
  avatar URL for Miku persona (always fresh, no cache lag)
- Pass avatar_url on every webhook.send() call in bipolar_mode.py,
  persona_dialogue.py, and api.py so avatars always match current pfp
  regardless of webhook cache state

bot/utils/persona_dialogue.py

@@ -881,7 +881,8 @@ This pushed things over the edge into a full argument."""
         from utils.bipolar_mode import (
             get_or_create_webhooks_for_channel,
             get_miku_display_name,
-            get_evil_miku_display_name
+            get_evil_miku_display_name,
+            get_persona_avatar_urls
         )
         
         webhooks = await get_or_create_webhooks_for_channel(channel)
@@ -891,9 +892,11 @@ This pushed things over the edge into a full argument."""
         
         webhook = webhooks["evil_miku"] if persona == "evil" else webhooks["miku"]
         display_name = get_evil_miku_display_name() if persona == "evil" else get_miku_display_name()
+        avatar_urls = get_persona_avatar_urls()
+        avatar_url = avatar_urls.get("evil_miku") if persona == "evil" else avatar_urls.get("miku")
         
         try:
-            await webhook.send(content=content, username=display_name)
+            await webhook.send(content=content, username=display_name, avatar_url=avatar_url)
         except Exception as e:
             logger.error(f"Error sending as {persona}: {e}")