fix(cli): drain stdout/stderr concurrently to prevent pipe deadlock

Sequential reads can deadlock when child process fills stderr pipe
buffer (~64KB) before stdout is consumed. Use Promise.all to drain
both streams in parallel.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: CarlosZiegler

packages/cli/src/lib/helpers.ts

@@ -94,8 +94,10 @@ export async function exec(
       stderr: "pipe",
     });
 
-    const stdout = await new Response(proc.stdout).text();
-    const stderr = await new Response(proc.stderr).text();
+    const [stdout, stderr] = await Promise.all([
+      new Response(proc.stdout).text(),
+      new Response(proc.stderr).text(),
+    ]);
     const exitCode = await proc.exited;
 
     return { stdout: stdout.trim(), stderr: stderr.trim(), exitCode };