Irreversible data migrations have no-op down() — migration:revert silently does nothing

[RUKAYAT-CODER]

These migrations deliberately wipe/transform data and their down() is a no-op:

• 1783000000000-clear-plaintext-auth-tokens.ts
• 1783000000001-reencrypt-oauth-provider-tokens.ts
• 1783000000003-clear-legacy-bcrypt-refresh-tokens.ts
• 1600000000000-enable-uuid-ossp.ts (extension only)

pnpm run migration:revert will report "reverted successfully" while actually doing nothing for these, which is easy to misread in CI or an incident. The no-op down is documented in code comments but not enforced anywhere.

Fix: at minimum, log a loud warning in down() (like fix-invoice-number-sequence does) so revert output is honest; consider a documented list of non-reversible migrations in the migrations README.

[Meet-hybrid]

I would like to contribute to this issue. I have experience with JavaScript/TypeScript, React, backend APIs, testing, Git, and software architecture. I will follow the acceptance criteria, add tests, and provide a focused pull request.