[Backport] update subscription panel for new designs (#6397)

## Summary
Backport of PR #6378 to `rh-test` branch.

## Changes
- Extract credit calculations into useSubscriptionCredits composable
- Extract action handlers into useSubscriptionActions composable
- Add comprehensive component and unit tests
- Update subscription panel layout to match Figma design exactly
- Add proper design tokens for modal card surfaces
- Update terminology from "API Nodes" to "Partner Nodes"
- Make credit breakdown dynamic with real API data
- Add proper loading states and error handling
- Remove unused tailwindcss eslint dependencies

## Conflicts Resolved
- Resolved merge conflicts in `packages/design-system/src/css/style.css`
related to button surface CSS variables

## Test plan
- Existing tests pass
- New tests for subscription composables and components

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6397-Backport-update-subscription-panel-for-new-designs-29c6d73d3650812aaa12ff242fd5e078)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: Johnpaul Chiwetelu <49923152+Myestery@users.noreply.github.com>

src/components/topbar/TopbarBadge.vue

@@ -37,7 +37,7 @@
         >
           {{ badge.label }}
         </div>
-        <div class="text-sm font-semibold">{{ badge.text }}</div>
+        <div class="text-sm font-inter">{{ badge.text }}</div>
         <div v-if="badge.tooltip" class="text-xs">
           {{ badge.tooltip }}
         </div>
@@ -90,7 +90,7 @@
         >
           {{ badge.label }}
         </div>
-        <div class="text-sm font-semibold">{{ badge.text }}</div>
+        <div class="text-sm font-inter">{{ badge.text }}</div>
         <div v-if="badge.tooltip" class="text-xs">
           {{ badge.tooltip }}
         </div>
@@ -117,7 +117,7 @@
     >
       {{ badge.label }}
     </div>
-    <div class="font-inter text-sm font-extrabold" :class="textClasses">
+    <div class="font-inter text-sm" :class="textClasses">
       {{ badge.text }}
     </div>
   </div>