feat(ui): add file explorer, TTS UI, views and routing

Add a file tree UI and corresponding composable for local file management.
Introduce TTS menu and player components for voice synthesis integration.
Add new EditorView and DocsView routes and update SettingsPanel view switching.
Enhance Mermaid plugin with improved styling and action buttons.

src/views/DocsView.vue

@@ -0,0 +1,40 @@
+<script setup>
+import { useSettingsStore } from '../stores/settings'
+
+const settings = useSettingsStore()
+const t = (key) => settings.t[key]
+</script>
+
+<template>
+  <div class="docs-view">
+    <div class="docs-empty">
+      <h2>{{ t('docsManagement') || '文档管理' }}</h2>
+      <p>{{ t('docsEmptyDesc') || '文档管理界面开发中...' }}</p>
+    </div>
+  </div>
+</template>
+
+<style scoped>
+.docs-view {
+  width: 100%;
+  height: 100%;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.docs-empty {
+  text-align: center;
+  color: var(--muted-text);
+}
+
+.docs-empty h2 {
+  font-size: 1.5rem;
+  margin-bottom: 0.5rem;
+  color: var(--app-text);
+}
+
+.docs-empty p {
+  font-size: 1rem;
+}
+</style>