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/build.gradle.kts

@@ -19,8 +19,8 @@ android {
         applicationId = "solutions.tretter.githugandroid"
         minSdk = 26
         targetSdk = 35
-        versionCode = 142
-        versionName = "0.1.141"
+        versionCode = 143
+        versionName = "0.1.142"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
         vectorDrawables.useSupportLibrary = true