Set up drf-spectacular for Swagger docs

[RossCabrera]

Overview

Configure drf-spectacular to automatically generate OpenAPI 3.0
schema and Swagger UI for all backend endpoints.

Requirements

• Configure in Django settings
• Add docstrings to all ViewSets
• Generate Swagger UI endpoint
• Test all endpoints in Swagger
• Configure Swagger UI styling

Acceptance Criteria

• drf-spectacular installed
• Swagger UI accessible at /api/docs/
• ReDoc accessible at /api/redoc/
• All endpoints documented
• Request/response examples shown
• Authentication documented
• Error codes documented
• Endpoint descriptions clear

Related Issues

• Blocks: Document all API endpoints #27