Modernize settings UI with Material Components, DayNight theme, and app icon

The screen was built entirely from raw android.widget.* views with no
theme applied at all, so it never had a chance to follow system dark/light
mode and looked dated regardless. Adds AppCompat + Material Components,
switches SettingsActivity to AppCompatActivity with a Theme.Material3.
DayNight theme, and rebuilds the screen with Material widgets (cards,
chips for the hidden-packages list, proper text fields).

Also adds a launcher icon (previously none): a vector adaptive icon, a
moon-like disc partially eclipsed by a diagonal veil in the background
color — no image tool involved, just XML.

Also renames the per-app "Remove" button to "Apply defaults (hide
everything)" — "Remove" read as removing the app from the list, not
resetting it to defaults, which is all it actually does.

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

app/src/main/AndroidManifest.xml

@@ -2,6 +2,9 @@
 
     <application
         android:label="@string/app_name"
+        android:icon="@mipmap/ic_launcher"
+        android:roundIcon="@mipmap/ic_launcher_round"
+        android:theme="@style/Theme.Veil"
         android:allowBackup="false"
         android:hasCode="true">
 
@@ -18,7 +21,8 @@
         <activity
             android:name=".SettingsActivity"
             android:exported="true"
-            android:label="@string/app_name">
+            android:label="@string/app_name"
+            android:theme="@style/Theme.Veil">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER" />