* fix(auth): sanitize unverified accounts during OAuth linking
- Add AccountSanitizationService for secure account cleanup
- Clear webhooks, API keys, credentials, and sessions for unverified accounts
- Reset password and 2FA settings during OAuth conversion
- Nullify redirect URLs on event types
Only affects accounts that never completed email verification
* fix(auth): block OAuth linking for unverified accounts
Replace sanitization with simpler blocking approach:
- Unverified CAL accounts cannot link to OAuth (Google/SAML)
- Add user-friendly error message with recovery path
- Remove AccountSanitizationService (no data loss risk)