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>

src/platform/workflow/sharing/components/ShareUrlCopyField.vue

@@ -0,0 +1,42 @@
+<template>
+  <div class="flex items-center gap-2">
+    <Input
+      readonly
+      :model-value="url"
+      :aria-label="$t('shareWorkflow.shareUrlLabel')"
+      class="flex-1"
+      @focus="($event.target as HTMLInputElement).select()"
+    />
+    <Button
+      variant="secondary"
+      size="lg"
+      class="font-normal"
+      @click="handleCopy"
+    >
+      {{
+        copied ? $t('shareWorkflow.linkCopied') : $t('shareWorkflow.copyLink')
+      }}
+      <i class="icon-[lucide--link] size-3.5" aria-hidden="true" />
+    </Button>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { refAutoReset } from '@vueuse/core'
+
+import Button from '@/components/ui/button/Button.vue'
+import Input from '@/components/ui/input/Input.vue'
+import { useCopyToClipboard } from '@/composables/useCopyToClipboard'
+
+const { url } = defineProps<{
+  url: string
+}>()
+
+const { copyToClipboard } = useCopyToClipboard()
+const copied = refAutoReset(false, 2000)
+
+async function handleCopy() {
+  await copyToClipboard(url)
+  copied.value = true
+}
+</script>