skill: add Android skills

.agents/skills/r8-analyzer/references/CONFIGURATION.md

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+To achieve maximum utilization of R8, the codebase must be configured correctly
+depending on the build script language (Kotlin DSL versus Groovy DSL).
+
+## 1. App Modules (`com.android.application`)
+
+The app's `build.gradle` or `build.gradle.kts` file must enable minification
+and resource shrinking within the `release` build type or the apps custom build
+type for release and performance testing. It MUST use the optimized default file
+(`proguard-android-optimize.txt`).
+
+**Kotlin DSL (`build.gradle.kts`):**
+
+    buildTypes {
+       getByName("release") {
+           isMinifyEnabled = true
+           isShrinkResources = true
+           proguardFiles(
+               getDefaultProguardFile("proguard-android-optimize.txt"),
+               "proguard-rules.pro"
+           )
+       }
+    }
+
+**Groovy DSL (`build.gradle`):**
+
+    buildTypes {
+       release {
+           minifyEnabled = true
+           shrinkResources = true
+           proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+       }
+    }
+
+## 2. `gradle.properties` Flags
+
+**Full Mode:** R8 Full Mode enables the entire optimizations
+
+- **AGP 8.0+** : Enabled by default. Ensure `android.enableR8.fullMode=false` is **NOT** present.
+- **Pre-AGP 8.0** : Explicitly enable with `android.enableR8.fullMode=true`.
+
+**Optimized Resource Shrinking:** If the AGP version of the project is less than
+9.0 and more than 8.6, explicitly enable the new resource shrinker:
+
+    android.r8.optimizedResourceShrinking=true