feat: add GitHub stars button to docs navbar and fix footer license

Add a star button with live count from the GitHub API in the top-right
of the docs site. Fix footer from "MIT License" to "AGPLv3 License".

apps/docs/.vitepress/theme/Layout.vue

@@ -0,0 +1,14 @@
+<script setup>
+import DefaultTheme from "vitepress/theme";
+import GitHubStars from "./GitHubStars.vue";
+
+const { Layout } = DefaultTheme;
+</script>
+
+<template>
+  <Layout>
+    <template #nav-bar-content-after>
+      <GitHubStars />
+    </template>
+  </Layout>
+</template>