[backport cloud/1.34] add shared comfy credit conversion helpers (#7293)

Backport of #7061 to `cloud/1.34`

Automatically created by backport workflow.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7293-backport-cloud-1-34-add-shared-comfy-credit-conversion-helpers-2c46d73d365081a9b1bcfb82462c3d7f)
by [Unito](https://www.unito.io)

Co-authored-by: Christian Byrne <cbyrne@comfy.org>
Co-authored-by: Claude <noreply@anthropic.com>

tests-ui/tests/composables/node/useCreditsBadge.test.ts

@@ -17,6 +17,14 @@ vi.mock('@/stores/workspace/colorPaletteStore', () => ({
   })
 }))
 
+vi.mock('@/composables/useFeatureFlags', () => ({
+  useFeatureFlags: () => ({
+    flags: {
+      subscriptionTiersEnabled: false // Test legacy badge behavior
+    }
+  })
+}))
+
 const { updateSubgraphCredits } = usePriceBadge()
 
 const mockNode = new LGraphNode('mock node')