test: add verify route tests and document the moderator, emeritus, and onboarding roles

[a-malik-gh]

Summary

This pull request closes #1408, #1480, #1481, and #1482.

Adds the missing email-verification verify route tests, and the three
governance documents the project was missing, each with a regression test
alongside it.

• src/app/api/auth/email-verification/verify/__tests__/route.test.ts — the
  GET and POST verify handlers, including the missing-token, expired-token, and
  failure paths.
• Governance/roles/MODERATOR.md and Governance/roles/MODERATOR.test.ts —
  moderator duties, moderation powers and limits, and the appointment and
  removal process.
• Governance/roles/EMERITUS.md and Governance/roles/EMERITUS.test.ts —
  emeritus status, the privileges retained and removed, and how the status is
  granted.
• Governance/processes/ONBOARDING.md and
  Governance/processes/ONBOARDING.test.ts — the onboarding steps, the
  resources a new contributor receives, and who owns onboarding.

The governance documents follow the conventions of the existing files in
Governance/: the same heading structure, a maximum line width of 82 columns,
and a ## Regression Tests section naming the companion test file. Each test
pins the document structure, the required content, the cross-references to
policies that already exist, and the line-width and placeholder rules, so the
documents cannot silently drift. Changes to the governance issues are limited
to the Governance/ folder.

Closes #1408
Closes #1480
Closes #1481
Closes #1482

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