fix(image): 编辑区相对路径图片显示解析（docs/16）

粘贴/插入的图片落盘与相对引用本身没问题，但编辑区从未解析相对路径：
页面在应用源下按相对路径取图必 404、只剩裂图。新增 image NodeView，
仅显示层把本地图片按文档目录归一化后经 read_file_base64 读成 data URL；
文档内容不变，Web 模式不启用。vitest 83 通过 + 2 跳过。

tests/image-display.test.ts

@@ -0,0 +1,72 @@
+// 图片显示解析回归：文档里的相对路径图片在编辑区经 NodeView 读成 data URL 显示；
+// 文档内容（序列化）保持相对路径不变。upload 插件以 instanceof 把关事件类型，
+// jsdom 缺 ClipboardEvent/DragEvent 全局，这里垫上。
+import { describe, it, expect } from 'vitest'
+import { createMarkdownEditor, getMarkdown } from '../src/editor/editor'
+import { editorViewCtx } from '@milkdown/kit/core'
+
+class FakeClipboardEvent extends Event {
+  clipboardData: unknown
+  constructor(type: string, init?: { clipboardData?: unknown }) {
+    super(type, { bubbles: true, cancelable: true })
+    this.clipboardData = init?.clipboardData
+  }
+}
+;(globalThis as Record<string, unknown>).ClipboardEvent = FakeClipboardEvent
+;(globalThis as Record<string, unknown>).DragEvent = class extends Event {}
+
+const tick = (ms = 40) => new Promise((r) => setTimeout(r, ms))
+
+describe('图片显示解析', () => {
+  it('相对路径图片在 DOM 里被换成 data URL，文档仍是相对路径', async () => {
+    const host = document.createElement('div')
+    document.body.appendChild(host)
+    const editor = createMarkdownEditor(host, '看图 ![截图](doc.assets/a.png) 完', {}, {
+      resolveImageDisplay: async (src) => (src === 'doc.assets/a.png' ? 'data:image/png;base64,QUJD' : null),
+    })
+    await editor.create()
+    await tick()
+    const img = host.querySelector('img:not(.ProseMirror-separator)')
+    expect(img?.getAttribute('src')).toBe('data:image/png;base64,QUJD')
+    expect(img?.getAttribute('alt')).toBe('截图')
+    expect(getMarkdown(editor)).toContain('![截图](doc.assets/a.png)')
+    await editor.destroy()
+    host.remove()
+  })
+
+  it('粘贴图片落盘为相对路径后同样能显示', async () => {
+    const host = document.createElement('div')
+    document.body.appendChild(host)
+    const editor = createMarkdownEditor(host, '正文', {}, {
+      onImageFile: async () => 'doc.assets/pasted.png',
+      resolveImageDisplay: async (src) => (src === 'doc.assets/pasted.png' ? 'data:image/png;base64,QUJD' : null),
+    })
+    await editor.create()
+    const view = editor.action((ctx) => ctx.get(editorViewCtx))
+    const file = new File(['png'], 'image.png', { type: 'image/png' })
+    const event = new FakeClipboardEvent('paste', {
+      clipboardData: { files: [file], items: [], getData: () => '' },
+    })
+    view.dom.dispatchEvent(event)
+    await tick(80)
+    expect(getMarkdown(editor)).toContain('doc.assets/pasted.png')
+    const img = host.querySelector('img:not(.ProseMirror-separator)')
+    expect(img?.getAttribute('src')).toBe('data:image/png;base64,QUJD')
+    await editor.destroy()
+    host.remove()
+  })
+
+  it('解析不到（文件缺失）时不崩溃、文档不变', async () => {
+    const host = document.createElement('div')
+    document.body.appendChild(host)
+    const editor = createMarkdownEditor(host, '![x](missing.png)', {}, {
+      resolveImageDisplay: async () => null,
+    })
+    await editor.create()
+    await tick()
+    expect(host.querySelector('img')).not.toBeNull()
+    expect(getMarkdown(editor)).toContain('![x](missing.png)')
+    await editor.destroy()
+    host.remove()
+  })
+})