feat: v0.2.1 — reference links, context menu, RTL, ja/ko, regex search, hooks, copy API

## Added
- Reference link/image resolution: [text][ref] + ![alt][ref] with [ref]: url definitions
- Right-click context menu: undo/redo/cut/copy/paste/selectAll + custom items
- RTL CSS layout support for Arabic, Hebrew, Persian etc.
- Japanese (ja) and Korean (ko) locales with 60+ keys each
- Divider position localStorage persistence
- Regex search toggle in search/replace panel
- Export HTML with embedded CSS styles
- beforeChange / afterChange lifecycle hooks (instance + global)
- copyAsMarkdown() / copyAsHTML() clipboard APIs
- CHANGELOG.md, CONTRIBUTING.md, CI workflow (.github/workflows/ci.yml)
- 2 new test suites: index.test.ts, styles.test.ts (684 total tests, +74)

## Changed
- autoSave plugin: closure-based state per instance instead of this context
- Plugin install() now receives options as second argument
- RTL locale detection: now uses language prefix (ar-SA → RTL)
- Rollup dev mode: only builds UMD format
- prepublishOnly now includes typecheck + test
- Version bumped to 0.2.1

## Fixed
- [text][ref] now correctly renders as link (was raw text)
- ![alt][ref] no longer produces empty src
- autoSave plugin state isolation across multiple editor instances
- Footnote definitions no longer consumed by refDef handler

site/docs.html

@@ -336,6 +336,8 @@ MeEditor<span class="c-punc">.</span><span class="c-fn">setLocale</span><span cl
 <tr><td>表格</td><td><code>| a | b |</code></td><td>&lt;table&gt; + 列对齐</td></tr>
 <tr><td>链接 <span class="badge">v0.1.15</span></td><td><code>[**t**](url)</code></td><td>文本内支持行内格式</td></tr>
 <tr><td>图片</td><td><code>![alt](url)</code></td><td>&lt;img&gt;</td></tr>
+<tr><td>引用链接 <span class="badge">v0.2.1</span></td><td><code>[text][ref]</code> + <code>[ref]: url</code></td><td>&lt;a&gt; 引用式</td></tr>
+<tr><td>引用图片 <span class="badge">v0.2.1</span></td><td><code>![alt][ref]</code> + <code>[ref]: url</code></td><td>&lt;img&gt; 引用式</td></tr>
 <tr><td>自动链接</td><td><code>&lt;https://...&gt;</code></td><td>&lt;a&gt;</td></tr>
 <tr><td>数学公式</td><td><code>$E=mc^2$</code></td><td>&lt;span&gt; / &lt;div&gt;</td></tr>
 <tr><td>脚注</td><td><code>text[^1]</code></td><td>&lt;sup&gt; + 底部</td></tr>
@@ -431,7 +433,7 @@ i18nUtils<span class="c-punc">.</span><span class="c-fn">formatDate</span><span
 
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-    MetonaEditor v0.2.0 · TypeScript · <a href="https://git.metona.cn/MetonaTeam/MetonaEditor" target="_blank" rel="noopener">源码仓库</a> · MIT License
+    MetonaEditor v0.2.1 · TypeScript · <a href="https://git.metona.cn/MetonaTeam/MetonaEditor" target="_blank" rel="noopener">源码仓库</a> · MIT License
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