fix(credentials): mkdir before lock file; satisfy Prettier

acquireCredentialsLock now creates the credentials directory before
openSync on the lock path, so first-time setup on a fresh HOME no longer
throws ENOENT (fixes subprocess setup/auth tests). Add trailing newline
to credentials-write-child.mjs for format:check.

Author: SahilRakhaiya05

src/lib/credentials.ts

@@ -217,6 +217,9 @@ function withCredentialsLock<T>(credentialsPath: string, fn: () => T): T {
 
 function acquireCredentialsLock(credentialsPath: string): void {
   const lockPath = credentialsLockPath(credentialsPath);
+  // Ensure the credentials directory exists before creating the lock file.
+  // writeCredentialsAtomic also mkdirs, but only after the lock is held.
+  mkdirSync(dirname(lockPath), { recursive: true, mode: 0o700 });
   const deadline = Date.now() + CREDENTIALS_LOCK_MAX_WAIT_MS;
   while (Date.now() < deadline) {
     try {

test/helpers/credentials-write-child.mjs

@@ -9,4 +9,4 @@ if (!profile || !credentialsPath || !apiKey) {
   process.exit(1);
 }
 
-writeProfile(profile, { apiKey }, { path: credentialsPath });
+writeProfile(profile, { apiKey }, { path: credentialsPath });