skill: add Android skills

.agents/skills/agp-9-upgrade/references/recipes.md

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+When migrating to AGP's new DSL, any Gradle code (plugins or logic in build
+scripts) that relied on the old DSL will stop working. Such code must be
+migrated.
+
+## Guidelines
+
+- **DO NOT** search the web for examples of how to do this. Use the **gradle-recipes** repository examples **only**.
+- **DO NOT** use AGP internals in migrated code.
+- **DO** use only public APIs in migrated code.
+
+In some cases, there is a one-to-one replacement for the old code. Some examples
+are in [the AGP 9.0.0 release notes](https://developer.android.com/build/releases/agp-9-0-0-release-notes).
+
+In other cases, there is no direct one-to-one replacement. For these situations,
+the [gradle-recipes repo](https://github.com/android/gradle-recipes) is a great resource. You can checkout one of its
+AGP 9.x branches, such as `agp-9.0`, `agp-9.1`, or `agp-9.2`. These branches
+contain recipes for common situations in Android projects. The following table
+lists the compatibility for recipes for each version of AGP.
+
+## Compatibility table
+
+| AGP version | gradle-recipes branch |
+|---|---|
+| 9.0.x | agp-9.0 |
+| 9.1.x | agp-9.1 |
+| 9.2.x | agp-9.2 |
+
+## Recipes and use-cases
+
+The following table links use-cases to recipes.
+
+| Recipe | Use-case |
+|---|---|
+| addCustomBuildConfigFields | Add custom BuildConfig fields |
+| listenToArtifacts | Rename APK |
+
+Additional details for each use-case follow.
+
+### Add custom BuildConfig fields
+
+See the detailed guide at [BuildConfig](https://developer.android.com/agents/skills/build/agp/agp-9-upgrade/references/buildconfig).
+
+### Renaming an APK
+
+In the old DSL, an APK could be renamed very simply. Here's an example:
+
+    android {
+      applicationVariants.all {
+        outputs.all {
+          val output = this as com.android.build.gradle.api.ApkVariantOutput
+          val fileName = output.outputFileName
+          if (fileName.contains("release")) {
+            output.outputFileName = "my-cool-new-name.apk"
+          }
+        }
+      }
+    }
+
+However, with AGP 9 and the new DSL, `applicationVariants` is no longer
+available. You must instead react to artifact creation using the
+`androidComponents.onVariants` API. A complete example of this is available in
+the **gradle-recipes** repository in the `listenToArtifacts` recipe.