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/plugins/index.ts

@@ -0,0 +1,7 @@
+import type { MarkdownPlugin } from './types'
+
+/**
+ * Global plugin registry.
+ * Plugins can implement lifecycle hooks defined in {@link MarkdownPlugin}.
+ */
+export const plugins: MarkdownPlugin[] = []

src/plugins/types.ts

@@ -0,0 +1,21 @@
+export interface MarkdownPlugin {
+  /**
+   * Called during component setup. Allows plugin to initialize.
+   * @param context - an object that can be extended by plugins.
+   */
+  onSetup?(context: Record<string, any>): void
+
+  /**
+   * Called after markdown is parsed to HTML, before emitting.
+   * Allows plugin to modify the HTML.
+   * @param payload - contains original markdown and generated html.
+   */
+  onAfterParse?(payload: { markdown: string; html: string }): { html?: string }
+
+  /**
+   * Called right before the HTML is rendered (e.g., before v-html).
+   * Allows final adjustments.
+   * @param payload - contains html that will be rendered.
+   */
+  onBeforeRender?(payload: { html: string }): { html?: string }
+}