feat(account): deletion orchestration + step-up + gateway edge

Step-up: email accounts confirm with a mailed code (purpose=delete, no deeplink —
ConfirmByToken refuses a delete token so a stray click can't delete); platform-only
accounts type a fixed phrase (anti-impulse). Endpoints /user/delete/{request,confirm};
the confirm orchestration resigns active games, drops all-robot games, tombstones +
anonymizes the account (freeing its creds), and revokes its sessions — the tombstone is
the point of no return, the rest best-effort. Gateway account.delete.{request,confirm}
ops + fbs AccountDeleteConfirm/AccountDeleteRequestResult + branded ru/en delete email.
Integration tests cover the step-up (code + no-email) and the orchestration pieces.

ui/src/gen/fbs/scrabblefb.ts

@@ -1,5 +1,7 @@
 // automatically generated by the FlatBuffers compiler, do not modify
 
+export { AccountDeleteConfirm } from './scrabblefb/account-delete-confirm.js';
+export { AccountDeleteRequestResult } from './scrabblefb/account-delete-request-result.js';
 export { AccountRef } from './scrabblefb/account-ref.js';
 export { Ack } from './scrabblefb/ack.js';
 export { AlphabetEntry } from './scrabblefb/alphabet-entry.js';