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/layout/activity_login.xml

@@ -34,7 +34,7 @@
                     android:text="MiniABS"
                     android:textSize="@dimen/login_title"
                     android:textStyle="bold"
-                    android:textColor="@color/accent" />
+                    android:textColor="@color/accent_light" />
 
                 <TextView
                     android:layout_width="wrap_content"
@@ -82,7 +82,7 @@
             android:text="Conectar"
             android:textStyle="bold"
             android:textSize="@dimen/login_btn_text"
-            android:textColor="#121519" />
+            android:textColor="#FFFFFF" />
 
         <TextView
             android:id="@+id/status"
@@ -90,7 +90,7 @@
             android:layout_height="wrap_content"
             android:layout_marginTop="10dp"
             android:textSize="@dimen/login_status"
-            android:textColor="@color/accent" />
+            android:textColor="@color/accent_light" />
 
         <TextView
             android:layout_width="fill_parent"