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: agent <agent@bdeshi.space>

app/src/main/res/mipmap-anydpi-v26/ic_launcher_round.xml

@@ -0,0 +1,4 @@
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@color/ic_launcher_background" />
+    <foreground android:drawable="@drawable/ic_launcher_foreground" />
+</adaptive-icon>