Add Intro Quiz to client apps catalog

[colfin22]

Adds Intro Quiz — a self-hosted "guess the intro" music quiz for family game night built on a Navidrome library (Subsonic API, non-admin login, strictly read-only against the library). Phones join by scanning a QR code on the TV board; scoreboard, album art and audio cast to a Chromecast or Android TV.

• Open source (MIT), 15+ stars: https://github.com/colfin22/intro-quiz
• npm run validate:app intro-quiz passes with no errors or warnings
• Images converted to WebP, max 1200px; thumbnail is an app screenshot (not a logo)

[colfin22]

Just a nudge on this one. I think it may be stuck rather than waiting in the queue.

The two workflow runs on this PR have never started. They both show as action_required, which I think is the approval step that applies to a first time contributor. Because of that the PR shows no checks at all, so there is nothing for a reviewer to go on. If a maintainer can hit Approve and run, they should go green. I ran npm run validate:app locally and it passes, and the entry uses the same assets/apps/<name>/ layout as the other app submissions, with index.yaml, a thumbnail and five WebP screenshots inside the size limits.

Happy to change whatever is needed. And if a music quiz game is not really what the client apps catalog is for, that is a fair call. Just say so and I will close it myself rather than leave it sitting in your queue.

Thanks for Navidrome, and for keeping the catalog going.