Modify Board controller for Access validation

[magush27]

Update Board controller to handle boards with accessCode appropriately.

File: api/controllers/board.js

Tasks:

1. Modify getBoard function:
   • If board has accessCode, return 403 with message "This board requieres an access code"
   • Include requiresAccessCode flag and accessCode in response
2. Modify getPublicBoards function:
   • Add filter accessCode: null to exclude Access boards from public listing

Acceptance Criteria:

• Direct access to Cboard Access boards via standard board endpoint is blocked
• Cboard Access boards do not appear in public board searches