fix: resolve pydantic init error and auto-generate webhook callback URL

- Fix AttributeError by removing self.config assignment before super().__init__()
- Remove callback_base_url from adapter config (no longer needed)
- Add set_webhook_url() method, called by botmgr with auto-built URL
- Add gewechat to webhook URL display list in bot.py
- botmgr now passes webhook_prefix + bot_uuid to adapters via set_webhook_url()

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/langbot/pkg/api/http/service/bot.py

@@ -68,6 +68,7 @@ class BotService:
             'wecomcs',
             'LINE',
             'lark',
+            'gewechat',
         ]:
             webhook_prefix = self.ap.instance_config.data['api'].get('webhook_prefix', 'http://127.0.0.1:5300')
             extra_webhook_prefix = self.ap.instance_config.data['api'].get('extra_webhook_prefix', '')