test: Add Compose screenshot testing support

Integrate the experimental Android screenshot testing plugin into the `core:ui` module. This includes initial visual regression tests for Alert components and updates to the CI workflow for automated validation.

- core/ui: Add `AlertScreenshotTest` and screenshot test dependencies
- gradle.properties: Enable `android.experimental.enableScreenshotTest`
- libs.versions.toml: Add `com.android.compose.screenshot` plugin and validation API
- reusable-check.yml: Add screenshot validation tasks to GitHub Actions workflow

core/ui/build.gradle.kts

@@ -21,9 +21,13 @@ plugins {
     alias(libs.plugins.meshtastic.android.library.compose)
     alias(libs.plugins.meshtastic.android.library.flavors)
     alias(libs.plugins.meshtastic.hilt)
+    alias(libs.plugins.screenshot)
 }
 
-configure<LibraryExtension> { namespace = "org.meshtastic.core.ui" }
+configure<LibraryExtension> {
+    namespace = "org.meshtastic.core.ui"
+    experimentalProperties["android.experimental.enableScreenshotTest"] = true
+}
 
 dependencies {
     implementation(projects.core.common)
@@ -55,4 +59,7 @@ dependencies {
     androidTestImplementation(libs.androidx.test.runner)
 
     testImplementation(libs.junit)
+
+    screenshotTestImplementation(libs.screenshot.validation.api)
+    screenshotTestImplementation(libs.androidx.compose.ui.tooling)
 }

core/ui/src/screenshotTest/kotlin/org/meshtastic/core/ui/AlertScreenshotTest.kt

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2025-2026 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.core.ui
+
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.tooling.preview.Preview
+import com.android.tools.screenshot.PreviewTest
+import org.meshtastic.core.ui.util.PreviewTextAlert
+import org.meshtastic.core.ui.util.PreviewIconAlert
+import org.meshtastic.core.ui.util.PreviewHtmlAlert
+import org.meshtastic.core.ui.util.PreviewMultipleChoiceAlert
+import org.meshtastic.core.ui.util.PreviewComposableAlert
+
+class AlertScreenshotTest {
+
+    @PreviewTest
+    @Preview(showBackground = true)
+    @Composable
+    fun TextAlert() {
+        PreviewTextAlert()
+    }
+
+    @PreviewTest
+    @Preview(showBackground = true)
+    @Composable
+    fun IconAlert() {
+        PreviewIconAlert()
+    }
+
+    @PreviewTest
+    @Preview(showBackground = true)
+    @Composable
+    fun HtmlAlert() {
+        PreviewHtmlAlert()
+    }
+
+    @PreviewTest
+    @Preview(showBackground = true)
+    @Composable
+    fun MultipleChoiceAlert() {
+        PreviewMultipleChoiceAlert()
+    }
+
+    @PreviewTest
+    @Preview(showBackground = true)
+    @Composable
+    fun ComposableAlert() {
+        PreviewComposableAlert()
+    }
+}