Issue 106 - Implement Candidate model and routes

[ctlchan]

Features

• Implemented Candidate model that extends the User model using mongoose discriminators with additional details
• Implemented CRUD routes for /api/candidates
• Incorporated zod schemas to verify request bodies

Routes

GET /api/candidates

• Supports filtering by name, email, status, or groupIds via query parameters
• groupIds must be an array

GET /api/candidates/:id

POST /api/candidates

PUT /api/candidates/:id

• Supports updating: name, email, groupIds, resumeUrl, year, program
• Does not support updating the password

DELETE /api/candidates/:id

• Prevents deletion is Candidate has associated resources
• Current associated resource types: meetings and availabilities

GET /api/candidates/:id/availability