chore(android): install Android SDK + wire AGP 9.2.1 (toolchain proven)

Android SDK installed on this machine (cmdline-tools via brew;
platform-tools + platforms;android-35 + build-tools;35.0.0), local.properties
points Gradle at it (gitignored). Wired AGP 9.2.1 into the version catalog +
google() repos; proved the full chain by building a throwaway android-library
module against SDK 35 (AAR produced), then removed the probe.

Groundwork for AW2+: AGP plugins in the catalog, google() in settings, and the
working recipe in README (incl. the AGP-9-has-built-in-Kotlin gotcha — Android
modules apply ONLY the android plugin, never kotlin.android). Pure JVM modules
still green (218 tests). Framework module stubs stay gated until implemented.

android/settings.gradle.kts

@@ -1,8 +1,9 @@
 pluginManagement {
     repositories {
+        google()
         gradlePluginPortal()
         mavenCentral()
-        // google() is only needed by the Android-framework modules (see below).
+        // google() (above) serves AGP for the Android-framework modules.
         // It requires the Android Gradle Plugin / SDK, absent in this env.
     }
 }
@@ -12,6 +13,7 @@ dependencyResolutionManagement {
     // Modules must not declare their own repositories.
     repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
     repositories {
+        google()
         mavenCentral()
     }
     // The version catalog at gradle/libs.versions.toml is auto-registered as `libs`.
@@ -28,11 +30,14 @@ include(":client-tls")
 include(":test-support")
 
 // ── Android-framework modules ───────────────────────────────────────────────────
-// Scaffolded (dirs + build.gradle.kts stubs exist) but NOT included, because this
-// environment has NO Android SDK. Their build scripts apply `com.android.*`
-// plugins that cannot resolve here.
-// TODO(android-sdk): enable when an Android SDK is available.
-// include(":app")
-// include(":terminal-view")
-// include(":host-registry")
-// include(":client-tls-android")
+// The Android SDK IS now installed (see android/README.md → "Android SDK setup"),
+// and AGP 9.2.1 is proven to build against SDK 35 with Gradle 9.6.1. These stay
+// commented out only because their build.gradle.kts are still empty SCAFFOLD STUBS
+// — enable each as its real module is implemented (plan AW2+).
+// Recipe: apply `alias(libs.plugins.android.library)` ONLY (AGP 9 has built-in
+// Kotlin — do NOT add kotlin.android); android { namespace; compileSdk = 35;
+// defaultConfig { minSdk = 29 } }.
+// include(":app")               // AW4 — uses libs.plugins.android.application
+// include(":terminal-view")     // AW3
+// include(":host-registry")     // AW1/AW2 storage half
+// include(":client-tls-android") // AW1 framework half