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

tests/styles.test.ts

@@ -0,0 +1,109 @@
+/**
+ * styles.ts 单元测试
+ * 覆盖 injectStyles / updateStyles / removeStyles
+ */
+
+import { injectStyles, updateStyles, removeStyles, getSystemTheme, watchSystemTheme } from '../src/styles';
+
+describe('styles.ts - injectStyles', () => {
+  afterEach(() => {
+    removeStyles();
+  });
+
+  test('injectStyles 创建 <style> 元素', () => {
+    injectStyles();
+    const el = document.getElementById('metona-editor-styles');
+    expect(el).not.toBeNull();
+    expect(el!.tagName).toBe('STYLE');
+  });
+
+  test('injectStyles 重复调用不创建重复元素', () => {
+    injectStyles();
+    injectStyles();
+    const els = document.querySelectorAll('#metona-editor-styles');
+    expect(els.length).toBe(1);
+  });
+
+  test('注入的 CSS 包含编辑器样式规则', () => {
+    injectStyles();
+    const el = document.getElementById('metona-editor-styles');
+    const css = el!.textContent || '';
+    expect(css).toContain('.me-wrapper');
+    expect(css).toContain('.me-toolbar');
+    expect(css).toContain('.me-textarea');
+    expect(css).toContain('.me-preview');
+    expect(css).toContain('--md-bg');
+    expect(css).toContain('--md-accent');
+  });
+
+  test('注入的 CSS 包含 RTL 规则', () => {
+    injectStyles();
+    const el = document.getElementById('metona-editor-styles');
+    const css = el!.textContent || '';
+    expect(css).toContain('[dir=rtl]');
+  });
+
+  test('注入的 CSS 包含打印样式', () => {
+    injectStyles();
+    const el = document.getElementById('metona-editor-styles');
+    const css = el!.textContent || '';
+    expect(css).toContain('@media print');
+  });
+
+  test('注入的 CSS 包含 reduced-motion', () => {
+    injectStyles();
+    const el = document.getElementById('metona-editor-styles');
+    const css = el!.textContent || '';
+    expect(css).toContain('prefers-reduced-motion');
+  });
+});
+
+describe('styles.ts - updateStyles', () => {
+  afterEach(() => {
+    removeStyles();
+  });
+
+  test('updateStyles 更新已注入的样式', () => {
+    injectStyles();
+    const el = document.getElementById('metona-editor-styles')!;
+    const original = el.textContent;
+    updateStyles();
+    expect(el.textContent).toBe(original); // 内容一致
+  });
+
+  test('updateStyles 在未注入时自动注入', () => {
+    removeStyles();
+    expect(document.getElementById('metona-editor-styles')).toBeNull();
+    updateStyles();
+    expect(document.getElementById('metona-editor-styles')).not.toBeNull();
+  });
+});
+
+describe('styles.ts - removeStyles', () => {
+  test('removeStyles 移除样式元素', () => {
+    injectStyles();
+    expect(document.getElementById('metona-editor-styles')).not.toBeNull();
+    removeStyles();
+    expect(document.getElementById('metona-editor-styles')).toBeNull();
+  });
+
+  test('removeStyles 重复调用不抛错', () => {
+    removeStyles();
+    expect(() => removeStyles()).not.toThrow();
+  });
+});
+
+describe('styles.ts - getSystemTheme', () => {
+  test('返回 light 或 dark', () => {
+    const theme = getSystemTheme();
+    expect(['light', 'dark']).toContain(theme);
+  });
+});
+
+describe('styles.ts - watchSystemTheme', () => {
+  test('返回取消函数', () => {
+    const unsub = watchSystemTheme(() => {});
+    expect(typeof unsub).toBe('function');
+    unsub();
+  });
+});