Resolve "Security Configuration: Integrate with GraphQL API"

What does this MR do and why?

This MR integrates the security tracked refs feature with the actual GraphQL API backend by:

1. Removing the @client directive from the securityTrackedRefsQuery - queries now use the real backend instead of using local Apollo resolvers
2. Deleting mock resolver files that were used for local development and UI prototyping:
   • app/assets/javascripts/security_configuration/graphql/resolvers.js (empty CE stub)
   • ee/app/assets/javascripts/security_configuration/graphql/resolvers.js (mock data and pagination logic)
3. Simplifying Apollo client setup - removed custom resolvers and cache configuration that were only needed for the mock implementation

This change moves the feature from a client-side mock implementation to using the production GraphQL API, enabling real data to be displayed in the security configuration tracked refs list.

References

Related to #577520 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Make sure you have the FF enabled: http://gdk.test:3000/rails/features/vulnerabilities_across_contexts
2. Navigate to a project's Security Configuration page
3. Verify the tracked refs list loads data from the actual API:
   • Open browser DevTools → Network tab
   • Filter by "graphql"
   • Confirm you see a getSecurityTrackedRefs query being sent to the server (not resolved locally)
   • Hint: Per default the main branch should be displayed
4. Test pagination:
   • Navigate between pages
   • Verify data loads correctly for each page

MR acceptance checklist

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