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

src/i18n.js

@@ -1,7 +1,7 @@
 /**
  * MetonaEditor i18n - 国际化管理
  * @module i18n
- * @version 0.1.2
+ * @version 0.1.3
  * @description 多语言支持、语言切换和翻译管理
  */
 
@@ -20,14 +20,15 @@ export const getCurrentLocale = () => currentLocale;
  * 设置当前语言
  */
 export const setCurrentLocale = (locale) => {
-  if (!LOCALES[locale]) {
-    console.warn(`Locale "${locale}" not found, falling back to "${fallbackLocale}"`);
-    locale = fallbackLocale;
+  let target = locale;
+  if (!LOCALES[target]) {
+    console.warn(`Locale "${target}" not found, falling back to "${fallbackLocale}"`);
+    target = fallbackLocale;
   }
 
-  currentLocale = locale;
-  notifyLocaleListeners(locale);
-  saveLocale(locale);
+  currentLocale = target;
+  notifyLocaleListeners(target);
+  saveLocale(target);
 };
 
 /**