test(auth): add regression tests for relative OAuth2 URLs

[maruthang]

Description

Add regression tests to prevent the relative OAuth2 URL handling bug from recurring. The bug was introduced in v5.20.0 (commit 80d56c9) and fixed in v5.27.0/v5.30.3, but had no test coverage to prevent regression.

New tests cover:

• sanitizeUrl with various relative path patterns (./../, ../, ../../, ./, /, with query params)
• Full OAuth2 authorize flow with dot-relative paths combined with currentServer

Motivation and Context

Ref #10340

The original bug broke relative OAuth2 authorization URLs (e.g., ./../identity/connect/authorize). While the fix is already on master, there were no tests to prevent this from regressing again.

How Has This Been Tested?

• All 832 unit tests pass, including the 3 new test cases
• Tests verified against the current sanitizeUrl implementation

Screenshots (if appropriate):

N/A

Checklist

My PR contains...

• No code changes (src/ is unmodified: changes to documentation, CI, metadata, etc.)
• Dependency changes (any modification to dependencies in package.json)
• Bug fixes (non-breaking change which fixes an issue)
• Improvements (misc. changes to existing features)
• Features (non-breaking change which adds functionality)

My changes...

• are breaking changes to a public API (config options, System API, major UI change, etc).
• are breaking changes to a private API (Redux, component props, utility functions, etc.).
• are breaking changes to a developer API (npm script behavior changes, new dev system dependencies, etc).
• are not breaking changes.

Documentation

• My changes do not require a change to the project documentation.
• My changes require a change to the project documentation.
• If yes to above: I have updated the documentation accordingly.

Automated tests

• My changes can not or do not need to be tested.
• My changes can and should be tested by unit and/or integration tests.
• If yes to above: I have added tests to cover my changes.
• If yes to above: I have taken care to cover edge cases in my tests.
• All new and existing tests passed.