release: v0.1.3 — bug fixes, performance, hardening

Bug Fixes:
- fix(core): exec() now supports _customActions registered via addToolbarButton
- fix(core): _emit('focus'/'blur') no longer passes editor argument twice
- fix(core): getHTML() now triggers beforeRender/afterRender hooks
- fix(core): _wrapSelection defaults to 'text' instead of i18n placeholder
- fix(core): addToolbarButton onClick+action no longer double-fires
- fix(core): null-safety on focus/blur/enable/disable after destroy
- fix(parser): empty headings (# ) no longer produce empty <h1> tags
- fix(parser): slugify returns 'heading' fallback for empty/special inputs
- fix(i18n): setCurrentLocale no longer mutates input parameter
- fix(core): autofocus skipped when readOnly is enabled

Performance:
- perf(core): cache last rendered value, skip parsing when content unchanged
- perf(core): add refresh() API to force re-render after theme/locale changes

Hardening:
- feat(core): tabSize dynamically applied to textarea via style.tabSize
- feat(core): getStatus() now includes readOnly field

Tests:
- 7 new test cases: customActions, refresh, focus args, destroy safety,
  getStatus readOnly, autofocus+readOnly, slugify edge cases
- Total: 425 tests passing (+7 from v0.1.2)

Types:
- EditorStatus includes readOnly field
- MarkdownEditor.refresh() added to type definitions

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-0.1.2-blue.svg)](https://www.npmjs.com/package/@metona-team/metona-editor)
+[![npm version](https://img.shields.io/badge/version-0.1.3-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)