feat: add theme url param for dev page

[mxschll]

Description

Related links, issue #, if available: Related: cloudscape-design/components#4663

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 91.24%. Comparing base (25658cc) to head (401751a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #438      +/-   ##
==========================================
- Coverage   91.76%   91.24%   -0.53%     
==========================================
  Files          59       59              
  Lines        1724     1724              
  Branches      436      466      +30     
==========================================
- Hits         1582     1573       -9     
- Misses        142      151       +9     

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