feat(client/android): CI screenshot capture via Roborazzi

Play-listing/marketing screenshots of the Compose client rendered on the host JVM
by Roborazzi (Robolectric Native Graphics) — no emulator, GPU, KVM, host, or JNI
core. Five scenes render the REAL composables with embedded mock state under a
forced brand palette (Material You has no wallpaper to seed from on the JVM):
hosts grid, settings, TOFU + PIN dialogs, and the live stats HUD. Validated 5/5
locally.

- New JVM unit-test source set (app/src/test) + Roborazzi/Robolectric test deps;
  @Config(sdk=36) is mandatory (no android-all jar for compileSdk 37) and the
  animation clock is paused so a text-bearing scene reaches idle.
- kit: `-PskipRustBuild` skips the cargo-ndk native build so the JVM-only test job
  needs no Rust/NDK; normal APK/AAR builds are unchanged.
- Widen BrandDark / StatsOverlay to internal so the tests can use them.
- Standalone best-effort tag-gated workflow; PNGs upload as a 30-day artifact.

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

clients/android/kit/build.gradle.kts

@@ -99,6 +99,12 @@ val cargoNdkDebug = registerCargoNdk("cargoNdkDebug", release = false)
 val cargoNdkRelease = registerCargoNdk("cargoNdkRelease", release = true)
 
 afterEvaluate {
-    tasks.named("preDebugBuild").configure { dependsOn(cargoNdkDebug) }
-    tasks.named("preReleaseBuild").configure { dependsOn(cargoNdkRelease) }
+    // `-PskipRustBuild` skips the cargo-ndk native build — for JVM-only tasks (the Roborazzi
+    // screenshot unit tests render Compose on the JVM and never load libpunktfunk_android.so), so
+    // CI/local screenshot runs don't need the Rust toolchain or NDK. The native build stays wired
+    // for every normal APK/AAR build.
+    if (!project.hasProperty("skipRustBuild")) {
+        tasks.named("preDebugBuild").configure { dependsOn(cargoNdkDebug) }
+        tasks.named("preReleaseBuild").configure { dependsOn(cargoNdkRelease) }
+    }
 }