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/table.test.ts

@@ -0,0 +1,19 @@
+import { describe, expect, it } from 'vitest'
+import { createEditorState } from './index'
+import { setEditorFocus, tableField } from './table'
+
+const doc = '| a | b |\n| --- | --- |\n| 1 | 2 |\n\n正文'
+
+describe('表格渲染', () => {
+  it('光标在文首但编辑器未聚焦时，开头的表格仍渲染', () => {
+    const state = createEditorState({ doc })
+    expect(state.selection.main.head).toBe(0)
+    expect(state.field(tableField).size).toBe(1)
+  })
+  it('编辑器聚焦且光标在表格内时显示源码，移出后恢复渲染', () => {
+    let state = createEditorState({ doc }).update({ effects: setEditorFocus.of(true) }).state
+    expect(state.field(tableField).size).toBe(0)
+    state = state.update({ selection: { anchor: doc.length } }).state
+    expect(state.field(tableField).size).toBe(1)
+  })
+})