Fix: show the whole Add tag button in the Manage tags dialog

[DevMando]

Summary

In the Manage tags dialog (opened from the tag button on any MCP or skill row), the right side of the "Add tag" button was cut off. It now fits on the row in full.

What changed

• Add row layout: the name box, color picker and button used to sit side by side at fixed sizes. The name box was forced to at least 300px, and the three together needed more room than the dialog gives its content (about 500px), so the button ran past the edge. Now the color picker and the button get the space they need, and the name box takes whatever is left.
• No other behavior changes: adding, coloring and removing tags work the same as before.

Why this was done

Most of the button was hidden, so it was hard to tell it was there. That made adding a tag harder than it should be.

How it was tested

• The project compiles. The app wasn't running this build yet when the PR was opened.
• Worth a manual check before merging: open Manage tags… on the MCPs page and on the Skills page, and confirm the whole "Add tag" button shows and still adds a tag.

Notes

• Changelog: entry added under [Unreleased] → Fixed.