feat: publish the store assets, so Play's declaration has a video link

Play's foreground-service declaration asks for a *link* to the demonstration video, which means
something has to be reachable without a login. The simplest answer is to stop ignoring the assets
and let Gitea serve them, so the video, the twelve normalised screenshots and the
already-committed icon and feature graphic all live in the repository now and are downloadable at

  https://gitea.softwareapp-hb.de/fishfacegit/foto-duplicate-finder/raw/branch/main/<path>

That reverses the old "screenshots are never committed" rule, and the reason it is safe to reverse
is worth stating plainly: the library in every published frame is the *generated* one
(tools/make-demo-photos.py), never a real one. The phone set was re-checked frame by frame before
publishing - every thumbnail in it is a demo image and the only trace of the device's own
5,385-photo library is a count in the summary card. .gitignore and docs/STORE_LISTING.md say so
where the rule used to be, so the next person does not have to reconstruct why.

Still ignored, deliberately: the raw adb captures, the demo photos themselves, and the recording
script's milestone PNGs (store-assets/fgs-demo/checkpoint-*.png) - debugging aids, not assets.

.gitignore

@@ -26,7 +26,12 @@ keystore.properties
 fixtures/
 store-assets/raw-screenshots/
 demo-photos/
-store-assets/screenshots/
+
-# Recorded demonstrations for Play's declarations (a picture of the demo library, like the
+# Note that the *finished* store assets are not ignored: Play wants public links for some of them
-# screenshots, so it is built rather than stored)
+# (the foreground-service demonstration video), and the files a listing is made of belong beside
-store-assets/fgs-demo/
+# the code that produces them. So the icon, the feature graphic, `store-assets/screenshots/` and
+# `store-assets/fgs-demo/` are committed — everything visible in them comes from the generated
+# demo library (tools/make-demo-photos.py), so publishing them exposes nobody's photos. The
+# exception is the milestones the recording script saves along the way, which are debugging aids
+# rather than assets:
+store-assets/fgs-demo/checkpoint-*.png