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.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.64%. Comparing base (abe3580) to head (7fb0dfb).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4887   +/-   ##
=======================================
  Coverage   97.64%   97.64%           
=======================================
  Files         958      958           
  Lines       31247    31247           
  Branches    11536    11537    +1     
=======================================
  Hits        30510    30510           
+ Misses        730      690   -40     
- Partials        7       47   +40     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.