* Implement Mastodon-compatible roles
- `Account.role` should only be available through verify_credentials for checking current user's permissions
- `Account.role` now carries a Mastodon-compatible permissions bitmap and a marker for whether it should be shown to the public
- `Account.roles` added for *public* display roles (undocumented but stable since Mastodon 4.1)
- Web template now uses only public display roles (no user-visible change here, we already special-cased the `user` role)
* Handle verify_credentials case for default role
* Update JSON exact-match tests
* Address review comments
* Add blocks bit to admin permissions bitmap
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