ci: build custom packages instead of full system configs

Focus on packages that actually need caching:
- custom.* packages from packages/
- qt-pinned.jellyfin-media-player (qt5webengine)

Avoids unrelated build failures (steam) and is much faster.

.gitea/workflows/ci.yml

@@ -26,22 +26,22 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        machine:
-          - nix-book
-          - boxy
-          - zix790prors
-          - nix-deck
-          - john-endesktop
-          - live-usb
+        package:
+          - custom.claude-code
+          - custom.app-launcher-server
+          - custom.mcrcon-rbw
+          - custom.tea-rbw
+          - custom.rclone-torbox-setup
+          - qt-pinned.jellyfin-media-player
     steps:
       - uses: actions/checkout@v6
 
       - uses: https://git.johnogle.info/johno/gitea-actions/nix-setup@v1
 
-      - name: Build ${{ matrix.machine }}
+      - name: Build ${{ matrix.package }}
         id: build
         run: |
-          OUT_PATH=$(nix build .#nixosConfigurations.${{ matrix.machine }}.config.system.build.toplevel --no-link --print-out-paths)
+          OUT_PATH=$(nix build .#${{ matrix.package }} --no-link --print-out-paths)
           echo "out_path=$OUT_PATH" >> "$GITHUB_OUTPUT"
         env:
           NIX_CONFIG: "access-tokens = git.johnogle.info=${{ secrets.GITEA_ACCESS_TOKEN }}"