fix(a11y): Tag selection modal input visibility

[SychO9]

Fixes #0000

Changes proposed in this pull request:
The tag selection modal input contains misaligned selected tags and the cursor is not visible on the input. There is also no focus ring indicating that it is an input.

Screenshot

Before	After

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.