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

tests/parser.test.js

@@ -350,6 +350,11 @@ describe('slugify', () => {
   test('去除首尾连字符', () => {
     expect(slugify('-hello-')).toBe('hello');
   });
+
+  test('slugify 空/特殊字符输入返回兜底值', () => {
+    expect(slugify('')).toBe('heading');
+    expect(slugify('###')).toBe('heading');
+  });
 });
 
 describe('parseMarkdown - v0.1.2 新语法', () => {