[Block] Template/[id] APIs #46

API requirements for the template/[id] block.

• Create GET /api/v1/templates/:id to fetch template details, images, stars, and reviews.
• Create POST /api/v1/templates/:id/purchase (or clone) to add it to owned templates.
• Create POST /api/v1/templates/:id/reviews (only allowed after purchasing/using).
• Required Schema Structure: Add TemplateReview model (stars Int, text String) and UserOwnedTemplate model (many-to-many join table for purchases).