Update app launcher icons and store metadata

- Convert legacy PNG launcher icons to WebP format across all density buckets (hdpi to xxxhdpi) and add corresponding round icon variants.
- Update adaptive icon configuration in `mipmap-anydpi-v26` to use a defined color resource for the background and unify the monochrome layer.
- Add `ic_launcher-playstore.png` and update Fastlane metadata, including the app icon and promotional screenshots.

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

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
-  <background android:drawable="@drawable/ic_launcher_background_white"/>
-  <foreground android:drawable="@drawable/ic_launcher_foreground"/>
-  <monochrome android:drawable="@drawable/ic_launcher_monochrome"/>
+    <background android:drawable="@color/ic_launcher_background"/>
+    <foreground android:drawable="@drawable/ic_launcher_foreground"/>
+    <monochrome android:drawable="@drawable/ic_launcher_monochrome"/>
 </adaptive-icon>

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

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<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"/>
+    <monochrome android:drawable="@drawable/ic_launcher_monochrome"/>
+</adaptive-icon>

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

@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
-  <background android:drawable="@drawable/ic_launcher_background_white"/>
-  <foreground android:drawable="@drawable/ic_launcher_foreground"/>
-  <monochrome android:drawable="@drawable/ic_launcher_monochrome"/>
-</adaptive-icon>

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

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="ic_launcher_background">#FFFFFF</color>
+</resources>