Ensure CSP check always tears down Chrome when startup fails

[Copilot]

This PR addresses the specific review comment about orphaned Chrome processes in the CSP checker. If startBrowser() throws before the check loop begins, cleanup now still executes.

• Scope

  • Applies only the requested fix in apps/demos/utils/server/csp-check.js for review comment discussion_r3347213638.

• Change

  • Moved browser startup into the existing try block in main().
  • This guarantees stopBrowser() in finally runs even when startup fails.

• Behavior impact

  • Prevents leaked Chrome processes on debugger/bootstrap failures.
  • No functional changes to the normal CSP-check execution path.

try {
  await startBrowser();
  await runPool(...);
} finally {
  stopBrowser();
}