ci: downgrade artifact actions to v3 for Gitea GHES compatibility

upload-artifact@v4 and download-artifact@v4 are not supported on GHES.
Also drop merge-multiple (v4-only) and adjust release glob to artifacts/*/*.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -44,7 +44,7 @@ jobs:
           go build -trimpath -ldflags="-s -w" -o "dist/waste-daemon-${SUFFIX}${EXT}" ./cmd/daemon
           go build -trimpath -ldflags="-s -w" -o "dist/waste-anchor-${SUFFIX}${EXT}" ./cmd/anchor
 
-      - uses: actions/upload-artifact@v4
+      - uses: actions/upload-artifact@v3
         with:
           name: server-${{ matrix.goos }}-${{ matrix.goarch }}
           path: dist/
@@ -93,7 +93,7 @@ jobs:
           cd cmd/app
           wails build -trimpath -ldflags="-s -w" -o ../../dist/waste-linux-amd64
 
-      - uses: actions/upload-artifact@v4
+      - uses: actions/upload-artifact@v3
         with:
           name: desktop-linux-amd64
           path: dist/waste-linux-amd64
@@ -107,14 +107,13 @@ jobs:
     if: startsWith(github.ref, 'refs/tags/')
 
     steps:
-      - uses: actions/download-artifact@v4
+      - uses: actions/download-artifact@v3
         with:
           path: artifacts/
-          merge-multiple: true
 
       - name: Create release
         uses: https://gitea.com/actions/gitea-release-action@main
         with:
           token: ${{ secrets.RELEASE_TOKEN }}
-          files: artifacts/*
+          files: artifacts/*/*
           prerelease: ${{ contains(github.ref_name, '-') }}