Faster, smoother dashboard

Switching tabs on a waitlist page (Responses, Analytics, Form Editor, Credentials) is now instant — no re-fetch of the page underneath
Dashboard, waitlists, waitlist detail, tokens, and feedback pages show a loading placeholder shaped like the real page instead of a blank flash
Paging, searching, and filtering responses keeps the current rows on screen (dimmed, with a small spinner) instead of clearing the table while it loads
Every button that saves, deletes, or sends something now shows a busy state and can't be clicked twice
Deleting an entry or changing its status updates the table immediately, and reverts with a message if it fails