feat: refactor skills API and database schema

- Replaced file-based skill category loading with API calls in the GET and POST methods of the skills route.
- Added new `SkillsService` for handling skill category operations.
- Updated SQL initialization script to create `skill_categories`, `skills`, and `skill_links` tables with appropriate relationships.
- Enhanced `ApiClient` with methods for loading skill categories and creating new skills, improving API interaction.
- Introduced error handling for skill category creation and loading processes.

services/index.ts

@@ -11,5 +11,8 @@ export { EvaluationService, evaluationService } from "./evaluation-service";
 // Teams services (server-only)
 export { TeamsService } from "./teams-service";
 
+// Skills services (server-only)
+export { SkillsService } from "./skills-service";
+
 // API client (can be used client-side)
 export { ApiClient, apiClient } from "./api-client";