feat(persistence): fix QuotaExceededError and cross-workspace draft leakage (#8520)

## Summary

Completes the workflow persistence overhaul by integrating the new draft
system into the app and migrating existing data. Fixes two critical
bugs:

1. **QuotaExceededError** - localStorage fills up with workflow drafts,
breaking auto-save
2. **Cross-workspace data leakage** - Drafts from one ComfyUI instance
appear in another

## Changes

- **What**: 
- `useWorkflowPersistenceV2.ts` - Main composable that hooks into graph
changes with 512ms debounce
- `migrateV1toV2.ts` - One-time migration of existing drafts to the new
scoped format
  - Updated E2E tests for new storage key patterns
- **Why**: Users lose work when storage quota is exceeded, and see
confusing workflows from other instances

## How It Works

- **Workspace scoping**: Each ComfyUI instance (identified by server
URL) has isolated draft storage
- **LRU eviction**: When storage is full, oldest drafts are
automatically removed (keeps 32 most recent)
- **Tab isolation**: Each browser tab tracks its own active/open
workflows via sessionStorage
- **Debounced saves**: Graph changes are batched with 512ms delay to
reduce storage writes

## Migration

Existing V1 drafts are automatically migrated on first load. The
migration:
1. Reads drafts from old `Comfy.Workflow.*` keys
2. Converts to new workspace-scoped format
3. Cleans up old keys after successful migration

---
*Part 4 of 4 in the workflow persistence improvements stack*

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: Simula_r <18093452+simula-r@users.noreply.github.com>

browser_tests/tests/colorPalette.spec.ts

@@ -244,21 +244,9 @@ test.describe(
       await comfyPage.settings.setSetting('Comfy.Node.Opacity', 0.5)
       await comfyPage.settings.setSetting('Comfy.ColorPalette', 'light')
       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()
+      const parsed = await comfyPage.page.evaluate(() => {
+        return window['app'].graph.serialize()
+      })
       expect(parsed.nodes).toBeDefined()
       expect(Array.isArray(parsed.nodes)).toBe(true)
       for (const node of parsed.nodes) {

browser_tests/tests/interaction.spec.ts

@@ -736,6 +736,25 @@ test.describe('Load workflow', { tag: '@screenshot' }, () => {
     await expect(comfyPage.canvas).toHaveScreenshot(
       'single_ksampler_modified.png'
     )
+    // Wait for V2 persistence debounce to save the modified workflow
+    const start = Date.now()
+    await comfyPage.page.waitForFunction((since) => {
+      for (let i = 0; i < window.localStorage.length; i++) {
+        const key = window.localStorage.key(i)
+        if (!key?.startsWith('Comfy.Workflow.DraftIndex.v2:')) continue
+        const json = window.localStorage.getItem(key)
+        if (!json) continue
+        try {
+          const index = JSON.parse(json)
+          if (typeof index.updatedAt === 'number' && index.updatedAt >= since) {
+            return true
+          }
+        } catch {
+          // ignore
+        }
+      }
+      return false
+    }, start)
     await comfyPage.setup({ clearStorage: false })
     await expect(comfyPage.canvas).toHaveScreenshot(
       'single_ksampler_modified.png'
@@ -758,10 +777,17 @@ test.describe('Load workflow', { tag: '@screenshot' }, () => {
       await comfyPage.menu.topbar.triggerTopbarCommand(['New'])
       await comfyPage.menu.topbar.saveWorkflow(workflowB)
 
-      // Wait for localStorage to persist the workflow paths before reloading
-      await comfyPage.page.waitForFunction(
-        () => !!window.localStorage.getItem('Comfy.OpenWorkflowsPaths')
-      )
+      // Wait for sessionStorage to persist the workflow paths before reloading
+      // V2 persistence uses sessionStorage with client-scoped keys
+      await comfyPage.page.waitForFunction(() => {
+        for (let i = 0; i < window.sessionStorage.length; i++) {
+          const key = window.sessionStorage.key(i)
+          if (key?.startsWith('Comfy.Workflow.OpenPaths:')) {
+            return true
+          }
+        }
+        return false
+      })
       await comfyPage.setup({ clearStorage: false })
     })