change credits icons and tooltips (conditional on feature flag) (#7276)

This PR changes the credits icons and tooltips based on state of the
`subscription_tiers_enabled` feature flag.

When the flag is enabled (or undefined -- for local), the dollar icon is
replaced with the lucide-component icon in UserCredit and node price
badges (Partner Nodes), and a new tooltip row appears in
CurrentUserPopover displaying "Credits have been unified" with a
detailed hover tooltip explaining the credit unification across Partner
Nodes and Cloud workflows.

<img width="539" height="535" alt="image"
src="https://github.com/user-attachments/assets/7e952f9b-0abb-4979-85b7-0eecdeaf808c"
/>

Related:

- https://github.com/Comfy-Org/ComfyUI_frontend/pull/6115 (borrows badge
implementation from this PR)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7276-change-credits-icons-and-tooltips-conditional-on-feature-flag-2c46d73d365081809a6afd5861018a15)
by [Unito](https://www.unito.io)

src/composables/useFeatureFlags.ts

@@ -12,7 +12,8 @@ export enum ServerFeatureFlag {
   MANAGER_SUPPORTS_V4 = 'extension.manager.supports_v4',
   MODEL_UPLOAD_BUTTON_ENABLED = 'model_upload_button_enabled',
   ASSET_UPDATE_OPTIONS_ENABLED = 'asset_update_options_enabled',
-  PRIVATE_MODELS_ENABLED = 'private_models_enabled'
+  PRIVATE_MODELS_ENABLED = 'private_models_enabled',
+  SUBSCRIPTION_TIERS_ENABLED = 'subscription_tiers_enabled'
 }
 
 /**
@@ -55,6 +56,16 @@ export function useFeatureFlags() {
         remoteConfig.value.private_models_enabled ??
         api.getServerFeature(ServerFeatureFlag.PRIVATE_MODELS_ENABLED, false)
       )
+    },
+    get subscriptionTiersEnabled() {
+      // Check remote config first (from /api/features), fall back to websocket feature flags
+      return (
+        remoteConfig.value.subscription_tiers_enabled ??
+        api.getServerFeature(
+          ServerFeatureFlag.SUBSCRIPTION_TIERS_ENABLED,
+          false
+        )
+      )
     }
   })