serve assets and the store archive from gitea-watch (the GitHub repo is gone)

github.com/Worph/MetaAppStore answers 404, and with it every jsDelivr
cdn.jsdelivr.net/gh/Worph/MetaAppStore@main/ URL: the icons, thumbnails and
screenshots of all 44 apps were missing from the store listing, and the store
source in the README no longer downloaded.

- Asset URLs in every Apps/*/docker-compose.yml now point at
  https://gitea-watch.nsl.sh/metastar/MetaAppStore/raw/branch/main/Apps/{AppName}/
  (103 of the 109 distinct URLs checked: 200 image/png). The other 6, MetaGateway
  and MetaWatch screenshot-1..3, name files that have never been in this repo.
- README: the store source is https://gitea-watch.nsl.sh/metastar/MetaAppStore/archive/main.zip
  (public, checked to download anonymously).
- CLAUDE.md and CONTRIBUTING.md: the asset rule and its grep guard follow, so an
  import cannot bring back a jsDelivr URL unnoticed.

Apps/MetaFeederSciHub/docker-compose.yml

@@ -86,8 +86,8 @@ x-casaos:
   title:
     en_us: MetaFeeder · Sci-Hub
 
-  icon: https://cdn.jsdelivr.net/gh/Worph/MetaAppStore@main/Apps/MetaFeederSciHub/icon.png
-  thumbnail: https://cdn.jsdelivr.net/gh/Worph/MetaAppStore@main/Apps/MetaFeederSciHub/thumbnail.png
+  icon: https://gitea-watch.nsl.sh/metastar/MetaAppStore/raw/branch/main/Apps/MetaFeederSciHub/icon.png
+  thumbnail: https://gitea-watch.nsl.sh/metastar/MetaAppStore/raw/branch/main/Apps/MetaFeederSciHub/thumbnail.png
 
   store_app_id: metafeederscihub
   is_uncontrolled: false