Migrate projects endpoints to nexus service

[jeroenrinzema]

closes #71

[Copilot]

Pull request overview

This PR migrates project management endpoints from the legacy platform service to the nexus service, establishing projects as a first-class resource in the new API architecture.

Key changes:

• Adds project CRUD endpoints (list, create, get, update) to the admin API
• Implements project-admin relationship management and access control
• Enhances authentication to load admin context from database for authorization

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
services/nexus/oapi/resources.yml	Defines OpenAPI schemas and endpoints for project operations
services/nexus/oapi/resources_gen.go	Generated client and server code from OpenAPI specification
services/nexus/internal/store/projects.go	Implements project store methods with RBAC filtering and OAPI conversion
services/nexus/internal/store/providers.go	Adds helper method to check if project has providers
services/nexus/internal/http/controllers/v1/projects.go	Implements project CRUD handlers with authorization checks
services/nexus/internal/http/controllers/v1/projects_test.go	Comprehensive integration tests for project endpoints
services/nexus/internal/http/controllers/v1/controller.go	Registers projects controller in main controller
services/nexus/internal/http/http.go	Passes store to auth middleware for admin loading
services/nexus/internal/http/auth.go	Enhances auth to load admin from database and add to context
pkg/claim/rbac/admin.go	New package for RBAC admin context management