test(integration): generate sample app and run smoke check

[thopatevijay]

• Integration test generates app into tmp directory using sample IDL.

• Check that generated pages/instruction/* exists and a minimal build (next build) succeeds (or next dev start smoke check).

• Optionally mock wallet to run headless Playwright smoke.

Acceptance criteria

• Integration runner exits 0, files present and next build succeeds.

• CI job exists (optional gated due to heavy dependencies).