feat: manage fruits — full CRUD with images and synonyms (story #02)

Backend: domain structs, FruitRepository interface + pg implementation,
9 Echo v4 handlers (list/get/create/update/delete, image sub-resources),
migration 000002 (fruit_type ENUM, fruits, fruit_synonyms, fruit_images),
route-scoped BodyLimit("5M") for uploads, http.DetectContentType for serving.

Frontend: typed fetch API layer, Pinia setup-style fruitStore, FruitList
(paginated), FruitCreate, and FruitDetail (edit + synonyms editor + image
gallery). 25 backend unit tests + integration test; 18 frontend tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -5,6 +5,7 @@ A full-stack fruit-variety database (Go + Vue 3).
 ## Features
 
 - Users can view a "Hello, OSDB!" landing page that confirms the backend is reachable via the Vite proxy.
+- Users can create, view, edit, and delete fruit varieties, including managing synonyms and uploading images.
 
 ## Quick Start