feat: workflow sharing and ComfyHub publish flow (#8951)

## Summary

Add workflow sharing by URL and a multi-step ComfyHub publish wizard,
gated by feature flags and an optional profile gate.

## Changes

- **What**: Share dialog with URL generation and asset warnings;
ComfyHub publish wizard (Describe → Examples → Finish) with thumbnail
upload and tags; profile gate flow; shared workflow URL loader with
confirmation dialog
- **Dependencies**: None (new `sharing/` module under
`src/platform/workflow/`)

## Review Focus

- Three new feature flags: `workflow_sharing_enabled`,
`comfyhub_upload_enabled`, `comfyhub_profile_gate_enabled`
- Share service API contract and stale-share detection
(`workflowShareService.ts`)
- Publish wizard and profile gate state management
- Shared workflow URL loading and query-param preservation

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8951-feat-share-workflow-by-URL-30b6d73d3650813ebbfafdad775bfb33)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: github-actions <github-actions@github.com>
Co-authored-by: GitHub Action <action@github.com>

browser_tests/tests/sidebar/workflows.spec.ts

@@ -330,12 +330,9 @@ test.describe('Workflows sidebar', () => {
       .getPersistedItem('workflow1.json')
       .click({ button: 'right' })
     await comfyPage.contextMenu.clickMenuItem('Duplicate')
-    await comfyPage.nextFrame()
-
-    expect(await workflowsTab.getOpenedWorkflowNames()).toEqual([
-      '*Unsaved Workflow.json',
-      '*workflow1 (Copy).json'
-    ])
+    await expect
+      .poll(() => workflowsTab.getOpenedWorkflowNames())
+      .toEqual(['*Unsaved Workflow.json', '*workflow1 (Copy).json'])
   })
 
   test('Can drop workflow from workflows sidebar', async ({ comfyPage }) => {