feat: v0.2.3 — 浮动格式工具栏 + 10个新API + 德语翻译 + 类型修复

### Added
- 浮动格式工具栏：选中文本自动弹出 bold/italic/code/link/strikethrough
- 10 个新 API: getSelectedText/getCursorPosition/setCursorPosition/scrollToLine/selectLine/selectAll/replaceAll/replaceAllRegex/lineCount/getLine
- 2 个新事件: selectionChange / cursorMove
- 德语 (de) locale 完整翻译
- floatingToolbar 配置项（默认 true）

### Fixed
- onLinkClick 移除 as any，正式加入 EditorOptions/DEFAULTS
- 所有版本号统一为 0.2.3

### Tests
- core.test.ts: 183 → 214 (+31 tests)
- 总计 ~725 tests

src/i18n.ts

@@ -266,6 +266,7 @@ export const presetLocales = {
   ja: { name: '日本語', nativeName: '日本語', direction: 'ltr', translations: (LOCALES as any)['ja'] },
   ko: { name: '한국어', nativeName: '한국어', direction: 'ltr', translations: (LOCALES as any)['ko'] },
   fr: { name: 'Français', nativeName: 'Français', direction: 'ltr', translations: (LOCALES as any)['fr'] },
+  de: { name: 'Deutsch', nativeName: 'Deutsch', direction: 'ltr', translations: (LOCALES as any)['de'] },
 };
 
 export const i18nUtils = createI18nManager();