Add custom font styles and theme enhancements

- Created a new CSS file for font imports and defined font families for base, mono, strong, em, and h1 elements.
- Added a new JavaScript file to extend the default VitePress theme, incorporating a custom layout and a Vue component for enhanced functionality.
- Integrated Mermaid diagram support and included the necessary styles for it.

openwiki/theme/components/DocMetaEx.vue

@@ -0,0 +1,50 @@
+<script setup lang="ts">
+import { computed } from "vue";
+import { useData } from "vitepress";
+
+const { frontmatter } = useData();
+
+const source = computed(() => frontmatter.value?.source ?? null);
+const title = computed(() => frontmatter.value?.title ?? null);
+const abstract = computed(() => frontmatter.value?.abstract ?? null);
+
+const hasExtended = computed(
+  () => source.value || title.value || abstract.value,
+);
+</script>
+
+<template>
+  <div v-if="hasExtended" class="doc-meta-ex">
+    <div v-if="title" class="doc-meta-title">标题：{{ title }}</div>
+    <div v-if="source" class="doc-meta-source">
+      来源：<a :href="source" target="_blank" rel="noopener noreferrer">{{
+        source
+      }}</a>
+    </div>
+    <div v-if="abstract" class="doc-meta-abstract">摘要：{{ abstract }}</div>
+  </div>
+</template>
+
+<style scoped>
+.doc-meta-ex {
+  display: flex;
+  flex-direction: column;
+  line-height: 1.8;
+  gap: 8px;
+}
+
+.doc-meta-source {
+  font-size: 12px;
+  color: var(--vp-c-text-2);
+}
+
+.doc-meta-title {
+  font-size: 12px;
+  color: var(--vp-c-text-1);
+}
+
+.doc-meta-abstract {
+  font-size: 12px;
+  color: var(--vp-c-text-2);
+}
+</style>