refactor: wire helpers into ComfyPage and update test usages

Phase 2 of ComfyPage refactor:

- Add ToastHelper, DragDropHelper, CommandHelper instances to ComfyPage

- Remove migrated methods from ComfyPage (command, toast, dragDrop, workflow, canvasOps, nodeOps methods)

- Update all test files to use new helper paths

- Keep visibleToasts as passthrough getter for backward compatibility

Amp-Thread-ID: https://ampcode.com/threads/T-019c1666-ed27-773c-976a-07cc805d7a6c
Co-authored-by: Amp <amp@ampcode.com>

browser_tests/tests/mobileBaseline.spec.ts

@@ -7,7 +7,7 @@ test.describe(
   () => {
     test('@mobile empty canvas', async ({ comfyPage }) => {
       await comfyPage.settings.setSetting('Comfy.ConfirmClear', false)
-      await comfyPage.executeCommand('Comfy.ClearWorkflow')
+      await comfyPage.command.executeCommand('Comfy.ClearWorkflow')
       await expect(async () => {
         expect(await comfyPage.nodeOps.getGraphNodesCount()).toBe(0)
       }).toPass({ timeout: 5000 })