MBS-12986: Revise Weibo URL cleanup

[SHREESHANTH99]

Fix MBS-12986

Problem

Some Weibo URLs entered in edits use the /n/ path or lack www/HTTPS, e.g.:

https://weibo.com/n/username
http://weibo.com/u/123456789

These URLs are inconsistent and can cause broken links or unexpected behavior.

Solution

• Normalize /n/ URLs to the standard /u/ format.
• Ensure https://www prefix is added if missing.
• This makes all saved Weibo URLs consistent and valid.

Testing

• Manually tested in local Docker development setup (http://localhost:5000).
• Entered /n/ URLs and verified they are normalized to /u/ format with https://www.
• Non-Weibo URLs remain unchanged.
• Optional: can add JS unit tests for /n/ → /u/ normalization.

Notes

• No database changes required.
• Only small JS file changes in root/static/scripts/cleanup.js.

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[reosarevok]

I guess it's a good start to at least standardise these, even though it's still unclear whether they should be added or we should ask people to find and enter the equivalent /u link.