test(app): restore e2e playwright suite to green

- Fake gh stub now handles `gh pr view --json <fields>` by exiting 1
  with "no pull requests found for branch", matching the daemon's
  expected no-current-PR path; resolveCurrentPullRequestView no longer
  cascades failures across the suite.
- Rewrite the two post-setup script tests in workspace-setup-streaming
  to exercise explicit launch paths (UI scripts menu + daemon RPC) —
  39db3ea5 intentionally removed automatic post-setup script spawning.
- Harden terminal-alternate-screen synchronization: wait for the probe
  to observe alt-enter and alt-exit plus the final normal-screen marker
  before asserting, so the echoed command no longer races the alt-screen
  transition.

packages/app/e2e/global-setup.ts

@@ -220,6 +220,11 @@ if (args[0] === "pr" && args[1] === "list") {
   process.exit(0);
 }
 
+if (args[0] === "pr" && args[1] === "view" && args[2] === "--json" && args[3]) {
+  console.error("no pull requests found for branch");
+  process.exit(1);
+}
+
 if (args[0] === "issue" && args[1] === "list") {
   console.log("[]");
   process.exit(0);