Improve light/dark theme toggle

frontend/components/CrownIcon.svelte

@@ -0,0 +1,6 @@
+<script>
+  export let mastered;
+</script>
+{#if mastered}
+  👑
+{/if}

frontend/main.js

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+import CrownIcon from './components/CrownIcon.svelte';
+
+// Expose a function to mount the CrownIcon component globally
+// This allows Django templates to easily initialize Svelte components.
+window.mountCrownIcon = (selector, props) => {
+  const target = document.querySelector(selector);
+  if (target) {
+    new CrownIcon({
+      target: target,
+      props: props,
+    });
+  }
+};