release: v0.1.5 — theme system usability, extensibility, external theme following

feat(themes): comprehensive theme system enhancement
- Fix resolveTheme('auto') always resolves to system theme (no stale override)
- Add per-instance theme isolation via createInstanceTheme()
- Add MarkdownEditor.setTheme()/getTheme()/getThemeContext() instance methods
- Add 'themeChange' instance event with { theme, resolved, config } payload
- Multi-instance independent themes (no cross-contamination)

feat(themes): external theme following (v0.1.5)
- followExternalTheme() — follow theme via data attr, CSS class, or callback
- adoptFromParent() — inherit theme from parent container
- watch() — watch external theme source (function or selector)

feat(themes): extensibility (v0.1.5)
- registerTheme() supports 'extends' option for theme inheritance
- exportCSSVars() — export all CSS variable values from element
- getCSSVariable() — query single CSS variable
- applyThemeToElement() — apply theme to any DOM element

chore: bump version 0.1.4 → 0.1.5 across all files
test(themes): 30 new tests covering all v0.1.5 theme APIs (499 total)

src/index.js

@@ -1,7 +1,7 @@
 /**
  * MetonaEditor - 轻量级 Markdown Editor 库
  * @module metona-editor
- * @version 0.1.4
+ * @version 0.1.5
  * @author thzxx
  * @description 现代化、零依赖、易扩展、易维护、易使用的 Markdown 编辑器库。单文件，开箱即用。
  * @license MIT
@@ -22,14 +22,14 @@
 
 import { MarkdownEditor } from './core.js';
 import { parseMarkdown, safeUrl, slugify, clearRenderCache } from './parser.js';
-import { themeUtils } from './themes.js';
+import { themeUtils, exportCSSVars, getCSSVariable, followExternalTheme, adoptFromParent, createInstanceTheme } from './themes.js';
 import { i18nUtils } from './i18n.js';
 import { pluginUtils, presetPlugins } from './plugins.js';
 import { animationUtils } from './animations.js';
 import { DEFAULTS, ICONS, THEMES, EDIT_MODES, DEFAULT_TOOLBAR, TOOLBAR_ACTIONS } from './constants.js';
 
 // 版本信息
-const VERSION = '0.1.4';
+const VERSION = '0.1.5';
 
 /**
  * 全局默认插件队列
@@ -202,6 +202,13 @@ const api = {
   plugins: pluginUtils,
   presetPlugins,
 
+  // 主题工具（v0.1.5 新增）
+  exportCSSVars,
+  getCSSVariable,
+  followExternalTheme,
+  adoptFromParent,
+  createInstanceTheme,
+
   // 常量
   DEFAULTS,
   ICONS,
@@ -240,6 +247,11 @@ export {
   pluginUtils,
   presetPlugins,
   animationUtils,
+  exportCSSVars,
+  getCSSVariable,
+  followExternalTheme,
+  adoptFromParent,
+  createInstanceTheme,
   DEFAULTS,
   ICONS,
   THEMES,