release: v0.4.0 — MetonaEditor 集成与架构重构

feat(editor): 将 Milkdown/ProseMirror 替换为 @metona-team/metona-editor v0.1.3
  - 三模式视图 (edit/split/preview) 由编辑器内置工具栏切换
  - searchReplace + imagePaste 预设插件
  - unified/rehype 渲染管线通过 render 钩子集成
  - 主题双向同步 (应用暗色模式 ↔ 编辑器主题)

feat(toast): metona-toast 迁移为 @metona-team/metona-toast v2.0.1

refactor: 删除冗余组件与代码
  - 移除 SourceEditor、Preview、SearchReplace、EditorToolbar、useMilkdown
  - 移除 StatusBar 组件及状态栏扩展架构（编辑器内置底栏替代）
  - 移除 useSettings、useStatusBarItem、useStatusBarItems、statusBarStore
  - 移除 EditMode/PreviewMode/SourceMode 图标

refactor(ui): 简化布局
  - 工具栏移除模式切换按钮，新增自动保存开关
  - useKeyboard 移除 Ctrl+1/2/3/B/I 快捷键
  - Editor 三模式统一由 MetonaEditor 容器渲染

chore: 版本号 v0.3.13 → v0.4.0
docs: 全面更新 README/DESIGN/CONTRIBUTING/DEVSETUP

src/renderer/stores/editorStore.ts

@@ -1,17 +1,17 @@
 import { create } from 'zustand'
-import type { EditorView } from '@milkdown/prose/view'
 import type { ViewMode } from '../types/settings'
+import type { MarkdownEditor } from '@metona-team/metona-editor'
 
-// Module-level getter/setter for the ProseMirror EditorView
+// Module-level getter for the MetonaEditor instance
 // Used by OutlinePanel for heading navigation
-let _getView: (() => EditorView | null) | null = null
+let _getEditor: (() => MarkdownEditor | null) | null = null
 
-export function setEditorViewGetter(fn: () => EditorView | null) {
-  _getView = fn
+export function setMetonaEditorGetter(fn: () => MarkdownEditor | null) {
+  _getEditor = fn
 }
 
-export function getEditorView(): EditorView | null {
-  return _getView ? _getView() : null
+export function getMetonaEditor(): MarkdownEditor | null {
+  return _getEditor ? _getEditor() : null
 }
 
 interface EditorState {