fix: log directory not created automatically

[dwmkerr]

Summary

When using --log-path with a path in a non-existent directory, the server fails with:

Error: ENOENT: no such file or directory, open '/tmp/shellwright/log.jsonl'

Root Cause

In src/index.ts, fsSync.appendFileSync(LOG_PATH, ...) is called without ensuring the parent directory exists first.

Fix

Add directory creation before first log write:

if (LOG_PATH) {
  const logDir = path.dirname(LOG_PATH);
  fsSync.mkdirSync(logDir, { recursive: true });
}