Refactor stats, add derived catalog stores, improve timer

src/lib/components/Reader/Timer.svelte

@@ -0,0 +1,12 @@
+<script lang="ts">
+  import { volumeStats } from '$lib/settings';
+
+  export let active = true;
+</script>
+
+<div
+  class:text-primary-700={!active}
+  class="mix-blend-difference z-10 fixed opacity-50 right-20 top-5 p-10 m-[-2.5rem]"
+>
+  <p>{active ? 'Timer active' : 'Timer idle'} | Minutes read: {$volumeStats?.timeReadInMinutes}</p>
+</div>