ci(release): pin upload/download-artifact to v3 for Gitea Actions

actions/upload-artifact@v4 and download-artifact@v4 require the
GitHub-hosted artifact backend, which Gitea Actions does not
implement (GHESNotSupportedError on v2.0.0+). Downgrade to v3.

v3's download-artifact has no merge-multiple flag and nests each
artifact under artifacts/<artifact-name>/, so the upload loop now
recurses to find the archives.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/release.yaml

@@ -76,7 +76,9 @@ jobs:
           echo "archive=$archive" >> "$GITHUB_OUTPUT"
 
       - name: Upload build artifact
-        uses: actions/upload-artifact@v4
+        # Gitea Actions doesn't support upload-artifact v4 (uses a
+        # GitHub-only backend API); pin to v3.
+        uses: actions/upload-artifact@v3
         with:
           name: nuwiki-ls-${{ matrix.target }}
           path: ${{ steps.package.outputs.archive }}
@@ -91,10 +93,11 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Download all build artifacts
-        uses: actions/download-artifact@v4
+        # Paired with upload-artifact@v3 above. v3 has no merge-multiple
+        # option and nests each artifact under its own subdirectory.
+        uses: actions/download-artifact@v3
         with:
           path: ./artifacts
-          merge-multiple: true
 
       - name: Ensure jq + curl
         run: |
@@ -135,7 +138,9 @@ jobs:
           fi
           echo "Created release id=$release_id"
 
-          for archive in artifacts/*.tar.gz; do
+          # download-artifact@v3 nests each artifact under its own dir
+          # (artifacts/<artifact-name>/<file>), so recurse.
+          for archive in $(find artifacts -name '*.tar.gz' -type f); do
             name="$(basename "$archive")"
             echo "Uploading $name …"
             curl --fail --silent --show-error \