M5: moderation, permissions, channel CRUD, in-app account management

- Server-side moderation & permissions (kick/ban/move/server-mute, channel CRUD).

- Database schema v2: channels, bans; BLAKE2b channel passwords, Argon2id accounts.

- C ABI additions and client-side handling (vc_kick_user, vc_ban_user, vc_set_permission, vc_set_server_mute, vc_move_user, vc_create/edit/delete_channel, vc_create/reset/delete/list_account).

- vccli flags for all M5 operations plus --username/--password auth.

- Four new tests covering permissions, kick/ban/move/mute, admin accounts, channel CRUD.

- Docs: protocol.md envelope updates, security.md channel-password hashing, PROGRESS.md.

core/src/session/session.h

@@ -51,6 +51,8 @@ struct User {
     std::string         nickname;
     bool                is_guest{true};
     uint32_t            channel_id{0};
+    bool                server_muted{false};
+    bool                server_deafened{false};
     std::vector<Stream> streams;
 };