feat(project): scaffold Vue 3 + Vite markdown editor

Add initial project structure including:
- .gitignore and VSCode settings
- Vite configuration and package.json with Vue 3 dependencies
- Basic HTML entry point and README update
- Core source files: App.vue, main.js, style.css
- Markdown editor component with plugin system and related types
- Sample HelloWorld component, router, and Pinia store
- Assets and SVG icons

This commit establishes the foundation for the Vue 3 application.

src/components/HelloWorld.vue

@@ -0,0 +1,43 @@
+<script setup>
+import { ref } from 'vue'
+
+defineProps({
+  msg: String,
+})
+
+const count = ref(0)
+</script>
+
+<template>
+  <h1>{{ msg }}</h1>
+
+  <div class="card">
+    <button type="button" @click="count++">count is {{ count }}</button>
+    <p>
+      Edit
+      <code>components/HelloWorld.vue</code> to test HMR
+    </p>
+  </div>
+
+  <p>
+    Check out
+    <a href="https://vuejs.org/guide/quick-start.html#local" target="_blank"
+      >create-vue</a
+    >, the official Vue + Vite starter
+  </p>
+  <p>
+    Learn more about IDE Support for Vue in the
+    <a
+      href="https://vuejs.org/guide/scaling-up/tooling.html#ide-support"
+      target="_blank"
+      >Vue Docs Scaling up Guide</a
+    >.
+  </p>
+  <p class="read-the-docs">Click on the Vite and Vue logos to learn more</p>
+</template>
+
+<style scoped>
+.read-the-docs {
+  color: #888;
+}
+</style>

src/components/MarkdownEditor.vue

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+<template>
+  <!-- Textarea for markdown input -->
+  <textarea
+    v-model="markdown"
+    @keydown="handleKeydown"
+    placeholder="Enter markdown..."
+    rows="10"
+    style="width: 100%;"
+  ></textarea>
+
+  <!-- Plugin host (no UI) -->
+  <PluginHost />
+</template>
+
+<script setup>
+import { ref, watch, onMounted } from 'vue'
+import { plugins } from '../plugins/index'
+import PluginHost from './PluginHost.vue'
+import markdownIt from 'markdown-it'
+import Prism from 'prismjs'
+// 按需加载常用语言
+import 'prismjs/components/prism-javascript'
+import 'prismjs/components/prism-python'
+import 'prismjs/components/prism-css'
+
+/* ---------- 插件挂载点 ---------- */
+const pluginContext = {}
+onMounted(() => {
+  plugins.forEach(p => {
+    if (p.onSetup) p.onSetup(pluginContext)
+  })
+})
+
+/* ---------- markdown 解析 ---------- */
+const md = markdownIt({
+  highlight: (code, lang) => {
+    if (lang && Prism.languages[lang]) {
+      return `<pre class="language-${lang}"><code>${Prism.highlight(
+        code,
+        Prism.languages[lang],
+        lang
+      )}</code></pre>`
+    }
+    return `<pre class="language-${lang}"><code>${md.utils.escapeHtml(
+      code
+    )}</code></pre>`
+  }
+})
+
+const markdown = ref('')
+
+/* ---------- 解析后钩子 & emit ---------- */
+watch(
+  markdown,
+  (newVal) => {
+    let html = md.render(newVal)
+
+    // onAfterParse 插件
+    const afterPayload = { markdown: newVal, html }
+    plugins.forEach(p => {
+      if (p.onAfterParse) {
+        const res = p.onAfterParse(afterPayload)
+        if (res && res.html) afterPayload.html = res.html
+      }
+    })
+
+    // onBeforeRender 插件
+    const beforePayload = { html: afterPayload.html }
+    plugins.forEach(p => {
+      if (p.onBeforeRender) {
+        const res = p.onBeforeRender(beforePayload)
+        if (res && res.html) beforePayload.html = res.html
+      }
+    })
+
+    emit('update:html', beforePayload.html)
+  },
+  { immediate: true }
+)
+
+/* ---------- 键盘快捷键 ---------- */
+function insertAtCursor(text) {
+  const el = document.activeElement
+  if (el && el.selectionStart !== undefined) {
+    const start = el.selectionStart
+    const end = el.selectionEnd
+    const before = markdown.value.slice(0, start)
+    const after = markdown.value.slice(end)
+    markdown.value = `${before}${text}${after}`
+    // 将光标放在插入文本后
+    const pos = start + text.length
+    nextTick(() => {
+      el.setSelectionRange(pos, pos)
+    })
+  }
+}
+
+function handleKeydown(e) {
+  if (e.ctrlKey && !e.shiftKey) {
+    if (e.key === 'b' || e.key === 'B') {
+      e.preventDefault()
+      insertAtCursor('**粗体**')
+    } else if (e.key === 'i' || e.key === 'I') {
+      e.preventDefault()
+      insertAtCursor('_斜体_')
+    } else if (e.key === '`') {
+      e.preventDefault()
+      insertAtCursor('```\n代码块\n```')
+    }
+  }
+}
+</script>
+
+<style scoped>
+textarea {
+  font-family: inherit;
+  font-size: 1rem;
+  padding: 0.5rem;
+  box-sizing: border-box;
+}
+</style>

src/components/PluginHost.vue

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+<template>
+  <!-- PluginHost does not render UI; it only runs plugin lifecycle hooks -->
+</template>
+
+<script setup>
+import { onMounted } from 'vue'
+import { plugins } from '../plugins/index'
+
+/**
+ * Context object that can be extended by plugins during onSetup.
+ * Currently empty but can hold shared resources.
+ */
+const context = {}
+
+onMounted(() => {
+  // Invoke onSetup hook of each registered plugin
+  plugins.forEach(p => {
+    if (p.onSetup) {
+      p.onSetup(context)
+    }
+  })
+})
+</script>