ci: target this instance's nix runner

- run on the 'nix' label with Nix preinstalled; drop the installer action
- replace the inline release API calls with vpm/publish.sh
- add curl to the devShell for the publish step

.gitea/workflows/ci.yml

@@ -7,35 +7,21 @@ on:
   workflow_dispatch:
 
 jobs:
-  build:
-    runs-on: ubuntu-latest
+  nix-flake:
+    name: Nix flake checks
+    runs-on: nix
     steps:
       - uses: actions/checkout@v4
 
-      - uses: cachix/install-nix-action@v27
-        with:
-          extra_nix_config: |
-            experimental-features = nix-command flakes
+      - name: Check flake
+        run: nix flake check --print-build-logs
 
-      # Builds the cdylib and runs the cargo tests (doCheck).
+      # package.sh bundles the cdylib from ./result/lib, so link the aac package first.
       - name: Build Rust core
         run: nix build .#aac --print-build-logs
 
-      # Rehearses the VPM release: stages the C# package, bundles libaac, updates vpm/index.json.
       - name: Package VPM zip
         run: nix develop -c ./vpm/package.sh
 
-      # The Unity bundle produced by the flake itself.
       - name: Build Unity bundle
         run: nix build .#default --print-build-logs
-
-      - name: Collect artifacts
-        run: |
-          mkdir -p dist
-          cp -L result dist/animator-as-crab-bundle.zip
-          cp vpm/dist/*.zip dist/
-
-      - uses: actions/upload-artifact@v3
-        with:
-          name: animator-as-crab
-          path: dist/*.zip