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>

res/drawable/seek_thumb.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="oval">
-    <solid android:color="@color/accent" />
+    <solid android:color="@color/accent_light" />
     <stroke android:width="2dp" android:color="@color/bg" />
     <size android:width="@dimen/seek_thumb" android:height="@dimen/seek_thumb" />
 </shape>