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)

types/index.d.ts

@@ -1,4 +1,4 @@
-// Type definitions for MetonaEditor v0.1.4
+// Type definitions for MetonaEditor v0.1.5
 // Project: https://git.metona.cn/MetonaTeam/MetonaEditor
 // Author: thzxx
 
@@ -201,6 +201,21 @@ export class MarkdownEditor {
   getStats(): EditorStats;
   getStatus(): EditorStatus;
 
+  // 主题（v0.1.5: 实例级主题管理）
+  setTheme(theme: ThemeName): this;
+  getTheme(): string;
+  getThemeContext(): {
+    get(): string;
+    set(theme: string): string;
+    toggle(): string;
+    getResolved(): string;
+    getConfig(): object;
+    getVars(): object;
+    syncWithElement(element: HTMLElement, opts?: object): () => void;
+    adopt(): () => void;
+    watch(source: Function | string): () => void;
+  } | null;
+
   // 插件
   use(plugin: string | PluginObject, options?: object): this;
   getPlugins(): PluginObject[];
@@ -307,7 +322,7 @@ export const themeUtils: {
   getCurrentTheme(): string;
   getResolvedTheme(): string;
   applyTheme(theme: ThemeName): void;
-  registerTheme(name: string, config: object): void;
+  registerTheme(name: string, config: { extends?: string; [key: string]: any }): void;
   unregisterTheme(name: string): void;
   getAllThemes(): object;
   getThemeNames(): string[];
@@ -317,6 +332,14 @@ export const themeUtils: {
   addThemeListener(fn: (theme: string, resolved: string) => void): () => void;
   removeThemeListener(fn: (theme: string, resolved: string) => void): void;
   clearThemeListeners(): void;
+  // v0.1.5 新增
+  exportCSSVars(el?: HTMLElement): Record<string, string>;
+  getCSSVariable(name: string, el?: HTMLElement): string;
+  applyThemeToElement(theme: string, target: HTMLElement): void;
+  followExternalTheme(opts: object, onChange: (theme: string) => void): () => void;
+  adoptFromParent(container: HTMLElement, onDetected: (theme: string) => void): () => void;
+  watch(source: Function | string, onChange: (theme: string) => void): () => void;
+  createInstanceTheme(editor: object): object;
   [key: string]: any;
 };