fix(authenticator): Make Verify User Skip button visible in dark mode

[VarshithaPamisetty]

Issue #, if available:
Fixes #5984

Description:

The Verify User "Skip" button hardcoded its text color to Theme.of(context).primaryColor, which is invisible in dark mode. Removing it lets the button inherit the TextButton default (colorScheme.primary), so it stays visible in both themes. Supersedes #6001 by @ekjotmultani.

Screenshots

Before (dark)	After (dark)

Tests

• Added a widget test asserting the Skip button doesn't hardcode a text color.
• Regenerated the verifyUser goldens; dart analyze and dart format clean.
• Verified the button is visible in dark mode after the fix.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.97%. Comparing base (b0c2048) to head (61b4dc3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7275      +/-   ##
==========================================
- Coverage   40.97%   40.97%   -0.01%     
==========================================
  Files         121      121              
  Lines        8273     8271       -2     
  Branches     3598     3598              
==========================================
- Hits         3390     3389       -1     
+ Misses       4883     4882       -1     

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