fix(reader): restore solid circle background on quick actions FAB

The Svelte 5 rewrite of QuickActions (replacing Flowbite's SpeedDial)
dropped the background/shadow on the toggle button, leaving only a
bare plus icon that disappears against light backgrounds.

Fixes #249

Author: Gnathonic

src/lib/components/Reader/QuickActions.svelte

@@ -153,7 +153,7 @@
     <!-- Main toggle button -->
     <button
       onclick={toggleMenu}
-      class="flex h-12 w-12 items-center justify-center rounded-full text-gray-900 focus:ring-2 focus:ring-blue-500 focus:outline-none dark:text-white"
+      class="flex h-12 w-12 items-center justify-center rounded-full bg-gray-700 text-gray-300 shadow-lg hover:bg-gray-600 focus:ring-2 focus:ring-blue-500 focus:outline-none dark:bg-gray-700 dark:text-gray-300 dark:hover:bg-gray-600"
       aria-label="Quick actions menu"
       style="transition: transform 0.3s ease; transform: rotate({open ? 45 : 0}deg);"
     >