MiniABS 1.5: Audiobookshelf icon and purple theme

- Launcher icon from the Audiobookshelf icon pack (art/icon_master_512.png),
  including an xhdpi size
- Notification icon cut out of the same artwork; player icons redrawn in the
  icon's lilac (tools/make_icons.py)
- Purple colour scheme taken from the icon: gradient accent buttons, lilac
  text accents (accent_light), purple-tinted backgrounds
- README: where the icon and colours come from

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

AndroidManifest.xml

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="com.miniabs"
-    android:versionCode="5"
-    android:versionName="1.4"
+    android:versionCode="6"
+    android:versionName="1.5"
     android:installLocation="auto">
 
     <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="10" />