fix: Improve primary button disabled state contrast in one-theme

[ywyyu17]

Description

Issue:
Loading spinners in primary variant disabled buttons have a color contrast ratio of 1.90:1, which fails the WCAG 3:1 minimum
contrast requirement for non-text graphical elements. Users with low vision have difficulty identifying this content.

Fix:
Updated the primary button disabled state tokens in one-theme (light mode only):

• colorBackgroundButtonPrimaryDisabled: neutral400 (#b7b7b7) → neutral150 (#f8f8f8)
• colorTextButtonPrimaryDisabled: neutral100 (#f9f9f9) → neutral500 (#909090)

New contrast ratio: 3:1 (#909090 on #f8f8f8), meeting the 3:1 requirement.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.66%. Comparing base (f066dd8) to head (e45fcb6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4887   +/-   ##
=======================================
  Coverage   97.66%   97.66%           
=======================================
  Files         958      958           
  Lines       31317    31317           
  Branches    11566    11566           
=======================================
  Hits        30585    30585           
  Misses        686      686           
  Partials       46       46           

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