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/locales/en/main.json

@@ -1852,7 +1852,11 @@
     "additionalInfo": "Additional Info",
     "model": "Model",
     "added": "Added",
-    "accountInitialized": "Account initialized"
+    "accountInitialized": "Account initialized",
+    "unified": {
+      "message": "Credits have been unified",
+      "tooltip": "We've unified payments across Comfy. Everything now runs on Comfy Credits:\n- Partner Nodes (formerly API nodes)\n- Cloud workflows\n\nYour existing Partner node balance has been converted into credits.\nLearn more here."
+    }
   },
   "subscription": {
     "title": "Subscription",