Implement Public Read-Only Endpoints for Collection Catalog

[vivjd]

Goal:
Expose read-only collection data to the public.

Tasks:

• GET /api/public/items – search and filter (platform, on-floor, text)
• GET /api/public/items/:id – show item details
• Exclude items where is_public_visible = false

Acceptance Criteria:

• Public can view items and filter/search correctly
• Hidden items never appear
• Pagination and search work smoothly