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

README.md

@@ -2,7 +2,7 @@
 
 > 轻量、零依赖、精致美观的 Markdown Editor 库。单文件，开箱即用，中文优先。
 
-[![npm version](https://img.shields.io/badge/version-0.1.1-blue.svg)](https://www.npmjs.com/package/@metona-team/metona-editor)
+[![npm version](https://img.shields.io/badge/version-0.1.2-blue.svg)](https://www.npmjs.com/package/@metona-team/metona-editor)
 [![license](https://img.shields.io/badge/license-MIT-green.svg)](./LICENSE)
 [![tests](https://img.shields.io/badge/tests-407%20passed-brightgreen.svg)](./tests)
 [![coverage](https://img.shields.io/badge/coverage-97%25-brightgreen.svg)](./tests)