Fix redo shortcut on Windows, table rendering at doc start, and save on tab close

- Bind Mod-Shift-z to redo on all platforms (CodeMirror only binds it on Linux/macOS)
- Render tables based on editor focus so a note starting with a table is not shown as source
- Send the save request without waiting for the IndexedDB draft write, and flush on pagehide;
  Firefox could drop the last edit when a tab was closed right after typing
- Fall back to clipboardData.items when pasting images with an empty files list

web/src/editor/keymap.test.ts

@@ -0,0 +1,20 @@
+// @vitest-environment happy-dom
+import { describe, expect, it } from 'vitest'
+
+describe('快捷键', () => {
+  it('Windows 上 Ctrl+Shift+Z 为重做', async () => {
+    // CodeMirror 在模块加载时读取平台，需先设置再导入
+    Object.defineProperty(navigator, 'platform', { value: 'Win32', configurable: true })
+    const { undo } = await import('@codemirror/commands')
+    const { EditorView, runScopeHandlers } = await import('@codemirror/view')
+    const { createEditorState } = await import('./index')
+    const view = new EditorView({ parent: document.body, state: createEditorState({ doc: '' }) })
+    view.dispatch({ changes: { from: 0, insert: 'abc' } })
+    undo(view)
+    expect(view.state.doc.toString()).toBe('')
+    const event = new KeyboardEvent('keydown', { key: 'Z', code: 'KeyZ', keyCode: 90, ctrlKey: true, shiftKey: true })
+    expect(runScopeHandlers(view, event, 'editor')).toBe(true)
+    expect(view.state.doc.toString()).toBe('abc')
+    view.destroy()
+  })
+})