test: add unit tests for getSessionWithToken utility

[saksham242007]

Closes #3100

Adds unit tests for getSessionWithToken in src/lib/get-session-token.ts, mocking next-auth's getServerSession and @/lib/resolve-user. Covers null-session, missing-field, and success cases including verifying accessToken is correctly populated.

[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

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• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

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• quality:exceptional — ×1.5 multiplier

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[Priyanshu-byte-coder]

The getSessionWithToken test itself is good — imports the real module and mocks deps cleanly. But this PR is scoped as a test PR yet also adds a new ScrollToTopButton component wired into the dashboard, plus an unrelated blank line in middleware.ts. Please drop those two so this stays a focused test PR (the scroll-to-top UI can go in its own PR). Once it's just the test + session?.user guard, happy to merge.