Feat: Persist all unsaved workflow tabs (#6050)

## Summary

- Keep all drafts in localStorage, mirroring the logic from VSCode.

- Fix a bug where newly created blank workflow tabs would incorrectly
restore as defaultGraph instead of blankGraph after page refresh.

Resolves https://github.com/Comfy-Org/desktop/issues/910, Resolves
https://github.com/Comfy-Org/ComfyUI_frontend/issues/4057, Fixes
https://github.com/Comfy-Org/ComfyUI_frontend/issues/3665

## Changes

### What
- Fix `restoreWorkflowTabsState` to parse and pass workflow data from
drafts when recreating temporary workflows
- Add error handling for invalid draft data with fallback to default
workflow
- Fix E2E test `should not serialize color adjustments in workflow` to
wait for workflow persistence before assertions
- Add proper validation for workflow nodes array in test assertions

### Breaking
- None

### Dependencies
- No new dependencies added

## Review Focus

1. **Workflow restoration**: Verify that blank workflows correctly
restore as blankGraph after page refresh
2. **Error handling**: Check that invalid draft data gracefully falls
back to default workflow
3. **Test coverage**: Ensure E2E test correctly waits for workflow
persistence before checking node properties
4. **Edge cases**: Test with multiple tabs, switching between tabs, and
rapid refresh scenarios

---------

Co-authored-by: Yourz <crazilou@vip.qq.com>

browser_tests/tests/colorPalette.spec.ts

@@ -232,11 +232,25 @@ test.describe('Node Color Adjustments', () => {
   }) => {
     await comfyPage.setSetting('Comfy.Node.Opacity', 0.5)
     await comfyPage.setSetting('Comfy.ColorPalette', 'light')
-    const saveWorkflowInterval = 1000
-    const workflow = await comfyPage.page.evaluate(() => {
-      return localStorage.getItem('workflow')
-    })
-    for (const node of JSON.parse(workflow ?? '{}').nodes) {
+    await comfyPage.nextFrame()
+    const parsed = await (
+      await comfyPage.page.waitForFunction(
+        () => {
+          const workflow = localStorage.getItem('workflow')
+          if (!workflow) return null
+          try {
+            const data = JSON.parse(workflow)
+            return Array.isArray(data?.nodes) ? data : null
+          } catch {
+            return null
+          }
+        },
+        { timeout: 3000 }
+      )
+    ).jsonValue()
+    expect(parsed.nodes).toBeDefined()
+    expect(Array.isArray(parsed.nodes)).toBe(true)
+    for (const node of parsed.nodes) {
       if (node.bgcolor) expect(node.bgcolor).not.toMatch(/hsla/)
       if (node.color) expect(node.color).not.toMatch(/hsla/)
     }