refactor: redesign v2 migration window UI with shadcn components

[kovsu]

What this PR does

Before this PR:

After this PR:

CleanShot.2026-03-17.at.17.21.20.mp4

Fixes #

Why we need it and why it was done in this way

The following tradeoffs were made:

The following alternatives were considered:

Links to places where the discussion took place:

Breaking changes

If this PR introduces breaking changes, please describe the changes and the impact on users.

Special notes for your reviewer

Checklist

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Approvers are expected to review this list.

• PR: The PR description is expressive enough and will help future contributors
• Code: Write code that humans can understand and Keep it simple
• Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• Documentation: A user-guide update was considered and is present (link) or not required. Check this only when the PR introduces or changes a user-facing feature or behavior.
• Self-review: I have reviewed my own code (e.g., via /gh-pr-review, gh pr diff, or GitHub UI) before requesting review from others

Release note

[EurFelux]

Note

This comment was translated by Claude.

This part is all a temporary design, but your design looks pretty good too 👍

@SiinXu let's see if it's OK

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Original Content

这部分都是临时设计，不过你这个设计也挺不错的👍

@SiinXu 看看是否 OK 吧