update subscription panel for new designs (#6378)

## Summary

Refactoring of subscription panel to improve maintainability and match
Figma design exactly. Extracted business logic into
`useSubscriptionCredits` and `useSubscriptionActions` composables, added
comprehensive testing, and enhanced the design system with proper
semantic tokens.

- Extract credit calculations and action handlers into reusable
composables
- Add component and unit tests with proper mocking patterns  
- Update terminology from "API Nodes" to "Partner Nodes"
- Make credit breakdown dynamic using real API data instead of hardcoded
values
- Add semantic design tokens for modal card surfaces with light/dark
theme support
- Reduce component complexity from ~100 lines to ~25 lines of logic
- Improve layout spacing, typography, and responsive behavior to match
Figma specs

<img width="1948" height="1494" alt="Selection_2220"
src="https://github.com/user-attachments/assets/b922582d-7edf-4884-b787-ad783c896b80"
/>

<img width="1948" height="1494" alt="Selection_2219"
src="https://github.com/user-attachments/assets/50a9f263-9adb-439d-8a89-94a498d394e3"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6378-update-subscription-panel-for-new-designs-29b6d73d3650815c9ce2c5977ac7f893)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/services/dialogService.ts

@@ -69,6 +69,7 @@ export const useDialogService = () => {
       | 'server-config'
       | 'user'
       | 'credits'
+      | 'subscription'
   ) {
     const props = panel ? { props: { defaultPanel: panel } } : undefined