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.

pkg/fbs/scrabble.fbs

@@ -507,6 +507,19 @@ table LinkUnlinkRequest {
   kind:string;
 }
 
+// AccountDeleteConfirm carries the account-deletion step-up proof: a mailed code (email
+// accounts) or the typed phrase (platform-only accounts).
+table AccountDeleteConfirm {
+  code:string;
+  phrase:string;
+}
+
+// AccountDeleteRequestResult reports which deletion step-up the account uses: "email"
+// (a code was mailed) or "phrase" (type the confirmation phrase).
+table AccountDeleteRequestResult {
+  method:string;
+}
+
 // LinkResult is the unified result of a confirm or merge step. status is "linked"
 // (bound to the caller), "merge_required" (the identity belongs to another account —
 // the secondary_* fields summarise it for the irreversible confirmation), or