chore(samples-android): Add optional SAGP build mode

Adds an optional useSagp flag to Android sample app builds that, when true, applies the Sentry Android Gradle Plugin. (Defaults to false, which matches existing build behavior.)

```
./gradlew :sentry-samples:sentry-samples-android:installDebug -PuseSagp=true
```

See the Android sample app README for more details.

Author: 0xadam-brown

sentry-samples/sentry-samples-android/README.md

@@ -0,0 +1,57 @@
+# Sentry Sample Android App
+
+Sample application demonstrating how to use the Sentry Android SDK, including core functionality (error reporting, tracing, session replay,
+profiling) and integrations (Compose, OkHttp, SQLDelight, etc.).
+
+## How to run it?
+
+Install the app on your device or emulator:
+
+```
+./gradlew :sentry-samples:sentry-samples-android:installDebug
+```
+
+or simply open the project in Android Studio and run the `sentry-samples-android` configuration.
+
+You can also apply the [Sentry Android Gradle Plugin](https://github.com/getsentry/sentry-android-gradle-plugin) (SAGP) when building (not applied by default):
+
+```
+./gradlew :sentry-samples:sentry-samples-android:installDebug -PuseSagp=true
+```
+
+In Android Studio, add `useSagp=true` to `gradle.properties` or pass it as a Gradle project property.
+
+## Build modes
+
+### With or without SAGP
+
+The sample app can be built with or without the SAGP.
+
+| Gradle Property | Required                 | Purpose                                                                                                        |
+|-----------------|--------------------------|----------------------------------------------------------------------------------------------------------------|
+| `useSagp`       | No (defaults to `false`) | When `true`, apply SAGP when building the sample app. When false or absent, build the sample app without SAGP. |
+
+You can configure SAGP properties via the lambda passed to `extensions.configure<SentryPluginExtension>("sentry")` in the sample app's
+`build.gradle.kts` file.
+
+### Builds against your local sentry-java branch
+
+Regardless of `useSagp`, the sample always depends on sentry-java modules from this monorepo (e.g., `projects.sentryAndroid`). SAGP's SDK
+auto-installation is disabled, so the sample never pulls a separate SDK version from Maven. Local SDK changes in your branch are picked up
+directly.
+
+## Viewing SDK output
+
+### Locally
+
+Debug builds enable SDK debug logging, so captured envelopes are printed to logcat (tag `Sentry`):
+
+```
+adb logcat -s Sentry
+```
+
+### On Sentry UI
+
+By default, SDK output produced by the sample app appears under the [sentry-sdk test project](https://sentry-sdks.sentry.io/issues/?project=5428559).
+To redirect them to your own project, replace the test DSN (i.e., the `io.sentry.dsn` `meta-data` value in `src/main/AndroidManifest.xml`
+with your own.

sentry-samples/sentry-samples-android/build.gradle.kts

@@ -1,12 +1,44 @@
 import com.android.build.api.artifact.SingleArtifact
 import com.android.build.api.variant.impl.VariantImpl
+import io.sentry.android.gradle.extensions.InstrumentationFeature
+import io.sentry.android.gradle.extensions.SentryPluginExtension
 import org.apache.tools.ant.taskdefs.condition.Os
 import org.gradle.internal.extensions.stdlib.capitalized
 
 plugins {
   id("com.android.application")
   alias(libs.plugins.kotlin.android)
   alias(libs.plugins.kotlin.compose)
+  alias(libs.plugins.sentry) apply false
+}
+
+val useSagp =
+  providers.gradleProperty("useSagp").map { it.equals("true", ignoreCase = true) }.orElse(false)
+
+if (useSagp.get()) {
+  apply(plugin = "io.sentry.android.gradle")
+}
+
+plugins.withId("io.sentry.android.gradle") {
+  // Extension configs match non-SAGP builds. Update locally to test your feature.
+  extensions.configure<SentryPluginExtension>("sentry") {
+    autoInstallation.enabled.set(false)
+    includeProguardMapping.set(false)
+    includeDependenciesReport.set(false)
+    telemetry.set(false)
+    tracingInstrumentation {
+      features.set(
+        setOf(
+          InstrumentationFeature.COMPOSE,
+          InstrumentationFeature.DATABASE,
+          InstrumentationFeature.FILE_IO,
+          InstrumentationFeature.OKHTTP,
+        )
+      )
+      logcat.enabled.set(false)
+      appStart.enabled.set(false)
+    }
+  }
 }
 
 android {