fix: use literal paths in Android CI expo prebuild cache key

Nested \${{ env.VAR }} inside hashFiles() string literals doesn't expand
in GitHub Actions, resulting in an empty hash and a stale cache hit on
every run. Use literal paths instead.

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

Author: msluszniak

.github/workflows/build-android-llm-example.yml

@@ -56,7 +56,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: ${{ env.WORKING_DIRECTORY }}/android
-          key: ${{ runner.os }}-expo-android-${{ hashFiles('${{ env.WORKING_DIRECTORY }}/app.json', '${{ env.WORKING_DIRECTORY }}/package.json') }}
+          key: ${{ runner.os }}-expo-android-${{ hashFiles('apps/llm/app.json', 'apps/llm/package.json') }}
           restore-keys: |
             ${{ runner.os }}-expo-android-
       - name: Generate native Android project