Add hidden diagnostic skin toggle

- Open a hidden diagnostics dialog after tapping the header seven times within fifteen seconds.
- Let the diagnostics dialog toggle the pane color/stripe skin on demand.
- Restore the normal app background and pane colors by default.
- Stop Scaffold from preserving the bottom navigation-bar inset while the keyboard is visible.
- Apply bottom navigation padding only when the IME is not open.

app/src/main/java/solutions/tretter/githugandroid/GitHugApp.kt

@@ -1,14 +1,18 @@
 package solutions.tretter.githugandroid
 
+import android.os.SystemClock
 import androidx.compose.foundation.background
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.WindowInsets
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
-import androidx.compose.foundation.layout.imePadding
+import androidx.compose.foundation.layout.ime
+import androidx.compose.foundation.layout.navigationBars
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.layout.statusBarsPadding
 import androidx.compose.foundation.verticalScroll
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Scaffold
@@ -26,6 +30,7 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.geometry.Rect
 import androidx.compose.ui.platform.LocalConfiguration
 import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.text.TextRange
 import androidx.compose.ui.text.input.TextFieldValue
 import androidx.compose.ui.unit.dp
@@ -37,6 +42,7 @@ fun GitHugApp() {
     MaterialTheme(colorScheme = GitHugColorScheme) {
         val context = LocalContext.current
         val configuration = LocalConfiguration.current
+        val density = LocalDensity.current
         val runtime = remember(context) { GitRepositoryRuntime(context.applicationContext) }
         if (!runtime.isNativeGitAvailable()) {
             MissingNativeGitScreen(message = runtime.unavailableMessage())
@@ -76,9 +82,18 @@ fun GitHugApp() {
         var showHelpOverlay by rememberSaveable { mutableStateOf(false) }
         var showHelpOnStart by rememberSaveable { mutableStateOf(true) }
         var helpPreferenceInitialized by rememberSaveable { mutableStateOf(false) }
+        var showDiagnosticDialog by rememberSaveable { mutableStateOf(false) }
+        var diagnosticSkinEnabled by rememberSaveable { mutableStateOf(false) }
+        var headerTapTimes by remember { mutableStateOf(emptyList<Long>()) }
         var exerciseBounds by remember { mutableStateOf<Rect?>(null) }
         var promptBounds by remember { mutableStateOf<Rect?>(null) }
         val currentLevel = levels[currentLevelIndex]
+        val appBackground = if (diagnosticSkinEnabled) DiagnosticAppBackground else AppBackground
+        val imeBottom = WindowInsets.ime.getBottom(density)
+        val navigationBottom = WindowInsets.navigationBars.getBottom(density)
+        val bottomSystemPadding = with(density) {
+            if (imeBottom > navigationBottom) 0.dp else navigationBottom.toDp()
+        }
 
         LaunchedEffect(solvedCelebrationTitle) {
             if (solvedCelebrationTitle != null) {
@@ -465,30 +480,50 @@ fun GitHugApp() {
             output = output + runtime.commandReferenceLines()
         }
 
-        Scaffold(containerColor = AppBackground) { padding ->
+        fun registerHeaderTap() {
+            val now = SystemClock.elapsedRealtime()
+            val recentTaps = (headerTapTimes + now).filter { tapTime -> now - tapTime <= 15_000L }
+            if (recentTaps.size >= 7) {
+                headerTapTimes = emptyList()
+                showDiagnosticDialog = true
+            } else {
+                headerTapTimes = recentTaps
+            }
+        }
+
+        Scaffold(
+            containerColor = appBackground,
+            contentWindowInsets = WindowInsets(0.dp),
+        ) { padding ->
             Surface(
                 modifier = Modifier
                     .fillMaxSize()
                     .padding(padding),
-                color = AppBackground,
+                color = appBackground,
             ) {
                 Box(modifier = Modifier.fillMaxSize()) {
                     Column(
                         modifier = Modifier
                             .fillMaxSize()
-                            .background(AppBackground)
-                            .imePadding()
+                            .background(appBackground)
+                            .statusBarsPadding()
                             .verticalScroll(screenScrollState)
-                            .padding(horizontal = 10.dp, vertical = 8.dp),
+                            .padding(
+                                start = 10.dp,
+                                top = 8.dp,
+                                end = 10.dp,
+                                bottom = 8.dp + bottomSystemPadding,
+                            ),
                         verticalArrangement = Arrangement.spacedBy(8.dp),
                     ) {
-                        FixedHeader()
+                        FixedHeader(onTap = { registerHeaderTap() })
                         Box(
                             modifier = Modifier.fillMaxWidth(),
                         ) {
                             PaneWorkspace(
                                 modifier = Modifier.fillMaxWidth(),
                                 paneLayout = paneLayout,
+                                diagnosticSkinEnabled = diagnosticSkinEnabled,
                                 onMovePane = { paneId, delta ->
                                     updatePaneLayout(transform = { layout -> movePane(layout, paneId, delta) })
                                 },
@@ -623,6 +658,14 @@ fun GitHugApp() {
             )
         }
 
+        if (showDiagnosticDialog) {
+            DiagnosticSkinDialog(
+                diagnosticSkinEnabled = diagnosticSkinEnabled,
+                onDiagnosticSkinEnabledChange = { diagnosticSkinEnabled = it },
+                onDismiss = { showDiagnosticDialog = false },
+            )
+        }
+
         solvedCelebrationTitle?.let { title ->
             SolvedCelebrationOverlay(title = title)
         }