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

site/demo.html

@@ -305,7 +305,7 @@
       '',
       '| 名称 | 值 |',
       '| --- | --- |',
-      '| 版本 | 0.1.1 |',
+      '| 版本 | 0.1.2 |',
       '| 依赖 | 零 |',
       '| 测试 | 390+ |',
       '',