fix(im): use tenant token for message history list

[xfcycc]

Summary

Fix Feishu IM message history reads by using tenant access token for im.v1.message.list.

• Switch conversation history and thread history list calls to tenant token
• Remove obsolete user-level get_as_user scopes from feishu_im_user_get_messages
• Keep feishu_im_user_search_messages on user token
• Document the bot-membership limitation for history reads

Closes #356

Why

im.v1.message.list only supports tenant access token. Calling it with user access token can fail with:

The app type is not supported

After switching to tenant token, the API still requires the bot to be in the target chat. This PR keeps that limitation explicit in tool descriptions.

Test plan

• pnpm build
• pnpm lint — no errors, 21 pre-existing warnings
• Manual: feishu_im_user_get_messages can read group history with tenant token in local patched runtime
• Manual/code review: feishu_im_user_search_messages remains user-token based

[CLAassistant]

All committers have signed the CLA.