fix: update Bilibili user and followings APIs

[coni233]

Summary

• Replace the retired Bilibili user-card API.
• Handle private following lists with a clear message.
• Show an in-image warning when Bilibili only exposes a partial following list.
• Accept Bilibili mobile copied UID formats such as UID:123456.

Testing

Tested manually with:

• public users with different UIDs, confirming results no longer reuse the same following list;
• users with private following lists;
• users whose followings are only partially exposed by Bilibili;
• plain UID and UID:-prefixed UID input.

Notes

Bilibili's current followings API may expose only part of a target user's following list. The rendered result image now displays this limitation.

Future work

This is not part of the current PR. We may explore whether third-party data-recording services such as Danmakus can provide public live-room-entry events as an additional signal for composition checks when Bilibili does not expose a complete following list.