fix(browser-detector): ignore Node.js even when navigator is defined (#6244)

[amodhakal]

Which problem is this PR solving?

BrowserDetector previously relied solely on the presence of navigator to detect browser environments.
Node.js >=21 defines navigator, which caused Node to be misclassified as a browser.

Fixes #6244

Short description of the changes

• Updated BrowserDetector to explicitly exclude Node.js from browser detection.
• Added a Node.js-specific regression test (BrowserDetector.node.test.ts) to verify that Node is never detected as a browser.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Added and passed new testing to not detect browser in Node.js even when navigator is defined.
• Existing browser tests remain unchanged and pass/skipped as expected.

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated (N/A)

[linux-foundation-easycla]

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• ✅ login: amodhakal / name: Amodh Dhakal (49dbcb6, 8e3260c)