CalDAV clients send only user+password over Basic Auth and can't provide a TOTP
code, so account passwords would bypass 2FA. Add revocable app passwords:
- models: AppPassword table (bcrypt hash, label, last_used); auto-created via
create_all
- profile_router: GET/POST/DELETE /profile/app-passwords (plaintext shown once)
- dav_router: Basic Auth accepts any app password; the account password is
accepted only when 2FA is disabled
- frontend: "App-Passwörter (CalDAV)" section in the profile modal (create/show-
once/copy/revoke) + i18n (de/en); login hint now says app password
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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