test: add colocated route tests for admin and email verification endpoints

[A6dulmalik]

Summary

This pull request closes #1403, #1405, #1406, and #1407.

Adds colocated route tests for the TeachLink Web admin feature-flag and
network-policy endpoints, and for the email-verification resend and restore
endpoints.

• src/app/api/admin/feature-flags/__tests__/route.test.ts — flag listing,
  creation, targeting-rule evaluation, and deletion behaviour.
• src/app/api/admin/network-policies/__tests__/route.test.ts — policy
  listing, scope/value/action validation, and the delete lifecycle.
• src/app/api/auth/email-verification/resend/__tests__/route.test.ts — the
  pending, already-verified, cooldown, and unknown-record responses.
• src/app/api/auth/email-verification/restore/__tests__/route.test.ts — the
  backup-code restore path and its rejection responses.

Each file lives beside the handler it covers, follows the existing test
conventions, and pins the status codes and error messages the routes already
return. No application code is modified.

Closes #1403
Closes #1405
Closes #1406
Closes #1407

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