feat: add functional authentication

spec/schemas/account/errors.ts

@@ -0,0 +1,7 @@
+import { ConflictError } from "@spec/relay/mod.ts";
+
+export class AccountEmailClaimedError extends ConflictError {
+  constructor(email: string) {
+    super(`Email '${email}' is already claimed by another account.`);
+  }
+}