Add GitHub repository selection endpoints and types

Introduces endpoints to list and update GitHub repositories for a project, adds a Repository type to the GitHub service, and refactors project admin access validation. Also adds the TaskManagerItem GraphQL type and links it to the Event type for improved integration with task managers like GitHub Issues.

Author: neSpecc

src/integrations/github/index.ts

@@ -5,7 +5,7 @@ import { ContextFactories } from '../../types/graphql';
 /**
  * Re-export types and service from service.ts for backward compatibility
  */
-export { GitHubService, IssueData, GitHubIssue, Installation } from './service';
+export { GitHubService, IssueData, GitHubIssue, Installation, Repository } from './service';
 
 /**
  * Append GitHub routes to Express app