Replace all browser dialogs with modern modal, add OIDC admin UI
- Add reusable showConfirm() modal component (supports plain confirm,
input prompt, danger styling, Enter key)
- Replace ALL 18 confirm() and prompt() calls across 8 JS files with
showConfirm() modal: admin user actions, session revoke, document
delete, template delete, milestone management, transcription settings
- Fix broken admin reset-password (btn was undefined in scope)
- Add OIDC/SSO configuration UI to Admin Panel (issuer, client ID/secret,
button label, disable local auth toggle, callback URL display)
5ec1ddec6b