refactor: rework API loader and caching

This commit removes dependency on rxjs.

It also implements better composables to handle data fetching from
remote APIs and caching these values more transparently.

This commit also switches from yarn to npm

It also switches to the official Umami plugin

content/.vuepress/components/FetchError.vue

@@ -0,0 +1,26 @@
+<template>
+  <div class="error rounded-corners card-width">
+    <p>API call to {{ props.url }} failed</p>
+  </div>
+</template>
+
+<script setup lang="ts">
+const props = defineProps({
+  url: {
+    required: true,
+    type: String,
+  },
+});
+</script>
+
+<style lang="less">
+@import 'node_modules/nord/src/lesscss/nord.less';
+@import '../styles/classes.less';
+
+.error {
+  display: inline-block;
+  padding: 2rem;
+  text-align: center;
+  background: @nord11;
+}
+</style>