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/AndroidManifest.xml

@@ -11,7 +11,8 @@
         android:theme="@style/Theme.GithugAndroid">
         <activity
             android:name=".MainActivity"
-            android:exported="true">
+            android:exported="true"
+            android:windowSoftInputMode="adjustResize">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER" />