release: v0.1.2 — readOnly, new syntax, plugins, optimizations

Features:
- feat(core): readOnly mode with config option and setReadOnly() API
- feat(parser): superscript ^text^ and subscript ~text~ support
- feat(parser): highlight/mark ==text== syntax
- feat(parser): table column alignment with colons (:---, :---:, ---:)
- feat(parser): emoji shortcodes 😄 → 😊 (80+ common emojis)
- feat(plugins): imagePaste preset — paste clipboard images as base64
- feat(core): instance-level beforeRender/afterRender events
- feat(styles): print stylesheet (@media print)
- feat(styles): mark element CSS styling
- feat(styles): readOnly mode CSS (.me-readonly)

Optimizations:
- perf(core): history debounce now configurable via historyDebounce option
- perf(core): skip _render() in edit-only mode (already guarded)
- fix(core): divider drag division-by-zero guard
- fix(core): config.style deep merge with DEFAULTS
- fix(core): scroll position preserved across mode switches

Tests:
- 9 new test cases: readOnly (3), parser syntax (6)
- Total: 418 tests passing (+9 from v0.1.1)

Chores:
- version bump 0.1.1 → 0.1.2
- TypeScript definitions updated for new APIs

src/constants.js

@@ -1,7 +1,7 @@
 /**
  * MetonaEditor Constants - 常量定义
  * @module constants
- * @version 0.1.1
+ * @version 0.1.2
  * @description 默认配置、主题、动画、工具栏等常量
  */
 
@@ -42,10 +42,14 @@ export const DEFAULTS = Object.freeze({
   spellcheck: false,
   // 历史栈上限
   historyLimit: 100,
+  // 历史栈防抖延迟（ms）
+  historyDebounce: 400,
   // 同步滚动（分屏模式）
   syncScroll: true,
   // 制表符插入的空格数（0 表示插入 \t）
   tabSize: 2,
+  // 只读模式
+  readOnly: false,
   // 主题：light / dark / auto / warm / 自定义
   theme: 'auto',
   // 国际化