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>

src/com/miniabs/Api.java

@@ -26,7 +26,7 @@ import android.os.Build;
 
 /** Audiobookshelf REST client (API as of server 2.x, including the 2.26+ token system). */
 final class Api {
-    static final String VERSION = "1.4";
+    static final String VERSION = "1.5";
 
     static class ApiException extends IOException {
         final int code;