fix(react): wrap loader in styledscope for consistent styling

[chakrihacker]

Problem

In Next.js with SSR, the server always rendered components with the default light theme, while the client-side React hydration would immediately switch to dark mode based on OS preference (prefers-color-scheme). This caused a hydration mismatch and a visible flash of incorrectly themed content on page load.

The root cause: the server has no access to window.matchMedia, so it cannot know the user's preferred color scheme at render time.

Solution

A cookie-based approach is used to bridge the server/client theme preference gap. The user's preferred theme is persisted to a theme-mode cookie, which the server can read on the next request to pre-render with the correct theme, eliminating the mismatch.

Before

After

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors

[rax7389]

Unit test Checks are failing in also the PR doesn't describe before and after fix

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.65%. Comparing base (20a6bc3) to head (e4ee495).

Additional details and impacted files

@@           Coverage Diff            @@
##             main     #174    +/-   ##
========================================
  Coverage   88.64%   88.65%            
========================================
  Files         154      154            
  Lines       13134    13140     +6     
  Branches     1716     1406   -310     
========================================
+ Hits        11643    11649     +6     
  Misses       1491     1491            

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