Fix instrumented test compilation after composable refactor

The Error composable was replaced by Placeholder and TopAppBar lost its
onNavigateUp parameter, but ErrorTest and TopAppBarTest were not
updated, so the androidTest sources no longer compiled. Rewrite
ErrorTest as PlaceholderTest against the new API (the action button is
now omitted entirely without a handler instead of rendered disabled)
and use showNavigationIcon in TopAppBarTest.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/src/androidTest/java/com/aurora/store/compose/composable/ErrorTest.kt

@@ -1,34 +0,0 @@
-/*
- * SPDX-FileCopyrightText: 2025 The Calyx Institute
- * SPDX-License-Identifier: GPL-3.0-or-later
- */
-
-package com.aurora.store.compose.composable
-
-import androidx.compose.ui.res.painterResource
-import androidx.compose.ui.test.assertHasClickAction
-import androidx.compose.ui.test.assertIsDisplayed
-import androidx.compose.ui.test.assertIsNotEnabled
-import androidx.compose.ui.test.onNodeWithText
-import com.aurora.store.IsolatedTest
-import com.aurora.store.R
-import org.junit.Test
-
-class ErrorTest : IsolatedTest() {
-
-    @Test
-    fun testErrorWithoutActionHandling() {
-        setContent {
-            Error(
-                painter = painterResource(R.drawable.ic_apps_outage),
-                message = "An error occurred!",
-                actionMessage = "Retry"
-            )
-        }
-
-        composeTestRule.onNodeWithText("Retry")
-            .assertIsDisplayed()
-            .assertHasClickAction()
-            .assertIsNotEnabled()
-    }
-}

app/src/androidTest/java/com/aurora/store/compose/composable/PlaceholderTest.kt

@@ -0,0 +1,54 @@
+/*
+ * SPDX-FileCopyrightText: 2025 The Calyx Institute
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+package com.aurora.store.compose.composable
+
+import androidx.compose.ui.res.painterResource
+import androidx.compose.ui.test.assertIsDisplayed
+import androidx.compose.ui.test.onNodeWithText
+import androidx.compose.ui.test.performClick
+import com.aurora.store.IsolatedTest
+import com.aurora.store.R
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class PlaceholderTest : IsolatedTest() {
+
+    @Test
+    fun testPlaceholderWithoutActionHandling() {
+        setContent {
+            Placeholder(
+                painter = painterResource(R.drawable.ic_apps_outage),
+                message = "An error occurred!",
+                actionLabel = "Retry"
+            )
+        }
+
+        composeTestRule.onNodeWithText("An error occurred!")
+            .assertIsDisplayed()
+
+        composeTestRule.onNodeWithText("Retry")
+            .assertDoesNotExist()
+    }
+
+    @Test
+    fun testPlaceholderActionClick() {
+        var clicked = false
+        setContent {
+            Placeholder(
+                painter = painterResource(R.drawable.ic_apps_outage),
+                message = "An error occurred!",
+                actionLabel = "Retry",
+                onAction = { clicked = true }
+            )
+        }
+
+        composeTestRule.onNodeWithText("Retry")
+            .assertIsDisplayed()
+            .performClick()
+
+        assertTrue(clicked)
+    }
+}

app/src/androidTest/java/com/aurora/store/compose/composable/TopAppBarTest.kt

@@ -16,7 +16,7 @@ class TopAppBarTest : IsolatedTest() {
     @Test
     fun testTitleWithNoNavigationAction() {
         setContent {
-            TopAppBar(title = "About", onNavigateUp = null)
+            TopAppBar(title = "About", showNavigationIcon = false)
         }
 
         composeTestRule.onNodeWithText("About")