test(compose): Robolectric JVM Compose testing infra + PoC (#373)

Enables unit-testing Jetpack Compose UI on the JVM via Robolectric, so
render-only screens can leave the jacocoNonJvmTestableSurface exclusion
list and be counted by JaCoCo without an emulator.

- add Robolectric 4.16.1 (test scope) + Compose ui-test-junit4/-manifest
- testOptions.unitTests.isIncludeAndroidResources = true so resources
  (strings, Material3 theme) resolve on the JVM
- src/test/resources/robolectric.properties pins sdk=36 (targetSdk 37 is
  a preview level Robolectric 4.16 has no sandbox for)
- PoC: AddAnotherAccountScreenJvmTest drives the screen with the v2
  createComposeRule under RobolectricTestRunner (3 tests, green on the JVM)
- drop AddAnotherAccountScreen from jacocoNonJvmTestableSurface (now
  JVM-covered); floor stays 0.79 — re-ratchet deferred to end of #373

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/test/kotlin/org/libremail/ui/onboarding/AddAnotherAccountScreenJvmTest.kt

@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+package org.libremail.ui.onboarding
+
+import android.content.Context
+import androidx.compose.ui.test.assertIsDisplayed
+import androidx.compose.ui.test.junit4.v2.createComposeRule
+import androidx.compose.ui.test.onNodeWithText
+import androidx.compose.ui.test.performClick
+import org.junit.Assert.assertTrue
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.libremail.R
+import org.libremail.ui.theme.LibreMailTheme
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.RuntimeEnvironment
+import org.robolectric.annotation.Config
+import org.robolectric.annotation.GraphicsMode
+
+/**
+ * Robolectric feasibility PoC (issue #373): proves Jetpack Compose UI can be unit-tested on the JVM
+ * without an emulator. `createComposeRule()` drives [AddAnotherAccountScreen] under
+ * [RobolectricTestRunner]; `stringResource(...)` and Material3 theming resolve because
+ * `testOptions.unitTests.isIncludeAndroidResources` is enabled in `app/build.gradle.kts`. Runs under
+ * `:app:testDebugUnitTest`, NOT `androidTest` — the instrumented `AddAnotherAccountScreenTest` stays.
+ *
+ * `@Config(sdk = [36])` because compileSdk/targetSdk 37 (preview) has no Robolectric 4.16 sandbox
+ * (also the default in `src/test/resources/robolectric.properties`); `@GraphicsMode(NATIVE)` is
+ * required for Compose to render under Robolectric.
+ */
+@RunWith(RobolectricTestRunner::class)
+@GraphicsMode(GraphicsMode.Mode.NATIVE)
+@Config(sdk = [36])
+class AddAnotherAccountScreenJvmTest {
+
+    @get:Rule
+    val composeTestRule = createComposeRule()
+
+    private val context: Context get() = RuntimeEnvironment.getApplication()
+
+    private fun string(resId: Int): String = context.getString(resId)
+
+    private fun setContent(onAddAnother: () -> Unit = {}, onFinish: () -> Unit = {}) {
+        composeTestRule.setContent {
+            LibreMailTheme(darkTheme = false, dynamicColor = false) {
+                AddAnotherAccountScreen(onAddAnother = onAddAnother, onFinish = onFinish)
+            }
+        }
+    }
+
+    @Test
+    fun rendersAccountAddedTitleFromResources() {
+        setContent()
+
+        // Proves the merged Android resource table loaded on the JVM (isIncludeAndroidResources).
+        composeTestRule.onNodeWithText(string(R.string.onboarding_account_added_title)).assertIsDisplayed()
+    }
+
+    @Test
+    fun tappingYes_invokesOnAddAnother() {
+        var addAnother = false
+        setContent(onAddAnother = { addAnother = true })
+
+        composeTestRule.onNodeWithText(string(R.string.onboarding_add_another_yes)).performClick()
+
+        assertTrue(addAnother)
+    }
+
+    @Test
+    fun tappingNo_invokesOnFinish() {
+        var finished = false
+        setContent(onFinish = { finished = true })
+
+        composeTestRule.onNodeWithText(string(R.string.onboarding_add_another_no)).performClick()
+
+        assertTrue(finished)
+    }
+}

app/src/test/resources/robolectric.properties

@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+# Default SDK for every Robolectric (JVM) test (issue #373). compileSdk/targetSdk are 37, a
+# preview level Robolectric 4.16.x does not ship a sandbox for; 36 (Baklava) is its newest
+# supported level and needs JDK 21 (the project's Gradle JDK). Individual tests may still override
+# with @Config(sdk = [..]). Only affects tests run with RobolectricTestRunner; plain JUnit unit
+# tests are unaffected.
+sdk=36