fix(data-exports): redirect guests to sign in

[pandemicsyn]

Summary

• Replace the /data-exports page's unauthenticated 404 with the standard protected-page sign-in redirect.
• Preserve /data-exports as the callback path so users following export-ready links return to the intended page after authentication.
• Update page-level regression coverage for both guest redirects and signed-in non-admin access.

Verification

• Manual browser verification was not performed because no local development stack or PostgreSQL service was available.

Visual Changes

Before	After
Unauthenticated visits to /data-exports render a 404 page.	Unauthenticated visits redirect to sign-in and return to /data-exports after authentication.

Reviewer Notes

• This uses the same getUserFromAuthOrRedirect pattern as other protected app pages and does not change authorization for signed-in users.
• The focused Jest file was discovered, but repository-wide test setup could not connect to the unavailable local PostgreSQL service before assertions ran.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (2 files)

• apps/web/src/app/(app)/data-exports/page.tsx
• apps/web/src/app/(app)/data-exports/page.test.ts

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_{Review guidance: REVIEW.md from base branch main}