[PR-27228] Upgrade Demo App target to Android 17 (API 37)

[dgtv]

Why

Google Play requires apps to target API 36+ by Aug 31, 2026 (target API level policy). This PR targets API 37 (Android 17, the latest stable release) instead of the minimum 36, so the app also clears the next annual deadline without another bump.

What changed

The actual requirement (app module only):

• app_target_sdk / app_compile_sdk: 35 → 37; app_version_code 3 → 4, versionName 1.0.1

SDK library — public contract unchanged: compileSdk/targetSdk 35, minSdk 16, version 0.5.14. The Play policy applies only to the uploaded app binary, and the SDK keeps its documented Android 4.1+ support, so no SDK release is part of this PR.

Toolchain cascade forced by compileSdk 37 (per the AGP compatibility table it needs AGP ≥ 9.1.1):

• AGP 8.5.2 → 9.3.0, Gradle 8.7 → 9.5.0, build-tools 37.0.0, unmock plugin 0.7.8 → 0.11.0
• Groovy DSL migration in both modules: AGP 9 removed compileSdkVersion/minSdkVersion/targetSdkVersion; = assignments replace the space syntax Gradle 10 removes; library targetSdk moved to testOptions (AGP 9 requirement)
• buildFeatures { buildConfig = true } in sdk replaces the removed android.defaults.buildfeatures.buildconfig flag; dropped android.enableJetifier (all deps are AndroidX)
• CircleCI image → cimg/android:2026.07.1 (JDK 21, SDK 37 preinstalled); removed-in-AGP-9 androidDependencies task replaced with :sdk:dependencies :app:dependencies
• proguard-android-optimize.txt replaces proguard-android.txt in both modules — AGP 9 rejects the old default file (inert while minifyEnabled = false)
• Test-only: PowerMock 1.6.6/Mockito 1.10.19 → PowerMock 2.0.9/Mockito 2.28.2 plus --add-opens test JVM args — the old stack cannot run on JDK 17+ (broken since CI dropped the Java 8 pin); full :sdk:test passes on JDK 21 with this toolchain
• New jitpack.yml pinning JDK 17 — JitPack's default JDK 8 can't run Gradle 9, which would have broken the next tagged release build

Draft until

• CI passes on this PR (build + :sdk:test verified locally on JDK 21 / Gradle 9.5 / AGP 9.3 / SDK 37)
• Android Studio sync (requires Studio Panda 3+ for API 37)
• Demo app pass on Android 17 — note targeting 36+ makes edge-to-edge mandatory, so check for UI drawing under system bars