fix: set solid dark green adaptive icon background to eliminate ring

Transparent background caused Pixel launcher to inject its own tinted
ring. Replace with #16703D (sampled from iOS icon background) so the
launcher shape-clips cleanly without any visible halo.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
-    <background android:drawable="@android:color/transparent"/>
+    <background android:drawable="@color/ic_launcher_background"/>
     <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
 </adaptive-icon>

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

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
-    <background android:drawable="@android:color/transparent"/>
+    <background android:drawable="@color/ic_launcher_background"/>
     <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
 </adaptive-icon>

app/src/main/res/values/themes.xml

@@ -1,5 +1,6 @@
 <resources>
     <color name="splash_bg">#000000</color>
+    <color name="ic_launcher_background">#16703D</color>
 
     <style name="Theme.Calendarr" parent="Theme.Material3.DayNight.NoActionBar">
         <!-- Black window/system bars (matches the app background). -->