[backport cloud/1.35] refactor: start on removing FF for subscription tiers (#7679)

## Summary

Backport of #7596 to cloud/1.35 branch.

**Original PR:** https://github.com/Comfy-Org/ComfyUI_frontend/pull/7596

### Changes
- Removes feature flag for subscription tiers
- Removes legacy code for non-subscription tier logic

### Conflict Resolution
- `src/renderer/extensions/vueNodes/components/NodeHeader.vue`: Took PR
version (simplified icon without FF conditional)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7679-backport-cloud-1-35-refactor-start-on-removing-FF-for-subscription-tiers-2cf6d73d365081a1ba41c135c84c2e7f)
by [Unito](https://www.unito.io)

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

@@ -1,8 +1,6 @@
 import { describe, expect, vi } from 'vitest'
 
 import { LGraphNode } from '@/lib/litegraph/src/litegraph'
-import type { LGraphBadge } from '@/lib/litegraph/src/LGraphBadge'
-import type { LGraphIcon } from '@/lib/litegraph/src/LGraphIcon'
 
 import { subgraphTest } from '../../litegraph/subgraph/fixtures/subgraphFixtures'
 
@@ -17,23 +15,10 @@ vi.mock('@/stores/workspace/colorPaletteStore', () => ({
   })
 }))
 
-vi.mock('@/composables/useFeatureFlags', () => ({
-  useFeatureFlags: () => ({
-    flags: {
-      subscriptionTiersEnabled: false // Test legacy badge behavior
-    }
-  })
-}))
-
-const { updateSubgraphCredits } = usePriceBadge()
+const { updateSubgraphCredits, getCreditsBadge } = usePriceBadge()
 
 const mockNode = new LGraphNode('mock node')
-const mockIcon: Partial<LGraphIcon> = { unicode: '\ue96b' }
-const badge: Partial<LGraphBadge> = {
-  icon: mockIcon as LGraphIcon,
-  text: '$0.05/Run'
-}
-mockNode.badges = [badge as LGraphBadge]
+mockNode.badges = [getCreditsBadge('$0.05/Run')]
 
 function getBadgeText(node: LGraphNode): string {
   const badge = node.badges[0]