pin the android sdk explicitly and apply review fixes

- flake: pin build-tools and platform-tools to 37.0.0 instead of "latest", matching build.gradle.kts
- robolectric: run at sdk 35 (targetSdk) and re-record the golden
- manifest: allowBackup off, drop not-yet-used permissions
- theme: drop no-op status/nav bar colors (edge-to-edge)
- deps: kotlin 2.1.20, drop unused deps and test runner
- wrapper: regenerate jar from 8.11.1, add distributionSha256Sum
- remove stale README

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,7 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 distributionUrl=https\://services.gradle.org/distributions/gradle-8.11.1-bin.zip
+distributionSha256Sum=f397b287023acdba1e9f6fc5ea72d22dd63669d59ed4a289a29b1a76eee151c6
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME