package-custom-app: fetch create-app-wasm.sh for the wasm target

score's create-app.sh now supports `--platform wasm` via a new
tools/create-app-wasm.sh; add it to the sparse-checkout so the action can
package custom apps for the browser.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019oPj1zRcxSQX7FNni7EHM6

Author: jcelerier

package-custom-app/action.yml

@@ -121,6 +121,7 @@ runs:
           tools/create-app-linux.sh
           tools/create-app-macos.sh
           tools/create-app-windows.sh
+          tools/create-app-wasm.sh
           tools/launcher/launcher.cpp
         sparse-checkout-cone-mode: false