ci: use upload-artifact@v3 (Gitea artifact backend compatibility)

upload-artifact@v4 uses the @actions/artifact v2 backend, which Gitea (reported
to the action as GHES) does not support. Pin to @v3, which uses the artifact
protocol Gitea implements. The exe itself now builds successfully; this was the
only remaining failure.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-windows.yml

@@ -106,7 +106,9 @@ jobs:
           Get-Item dist/macropad.exe | Format-List Name, Length, LastWriteTime
 
       - name: Upload build artifact
-        uses: actions/upload-artifact@v4
+        # v3 uses the artifact protocol Gitea supports; v4+ requires a backend
+        # Gitea (reported as GHES) does not provide.
+        uses: actions/upload-artifact@v3
         with:
           name: macropad-windows
           path: dist/macropad.exe