Fix GitHub Actions artifact upload for GHES compatibility

- Downgrade upload-artifact from v4 to v3 for GHES compatibility
- Remove include-hidden-files parameter (not available in v3)

GHES doesn't support the newer v4 actions yet.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

.forgejo/workflows/build.yml

@@ -31,8 +31,7 @@ jobs:
         run: npm run build
 
       - name: Upload Build Artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: obs-ss-build
-          include-hidden-files: 'true'
           path: ./.next/*