fix: visible focus ring for inverted links in One Theme (WCAG 2.4.11)

[Harsh-Anand-Singh]

Description

In One Theme, color="inverted" links used outside a visual context fall back to the colorBorderItemFocused ring, which resolves to the same Indigo600 primitive as the dark notification-style surfaces inverted links are designed for, making the keyboard focus ring invisible (1.00:1 on the link permutations page). Scope the inverted variant's ring fallback to currentColor under One Theme: the ring always matches the (already legible) inverted text color, guaranteeing >= 3:1 wherever the text itself passes, including light-mode flashbar/alert where a static light ring would fail.

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.66%. Comparing base (670d1fc) to head (b5b7163).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4903   +/-   ##
=======================================
  Coverage   97.66%   97.66%           
=======================================
  Files         958      958           
  Lines       31317    31317           
  Branches    11566    11565    -1     
=======================================
  Hits        30585    30585           
- Misses        686      725   +39     
+ Partials       46        7   -39     

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