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>

backend/internal/domain/fruit.go

@@ -0,0 +1,40 @@
+package domain
+
+import "time"
+
+type Fruit struct {
+	ID          int          `json:"id"`
+	Name        string       `json:"name"`
+	OSDBNumber  string       `json:"osdb_number"`
+	Comment     *string      `json:"comment"`
+	FruitType   string       `json:"fruit_type"`
+	Synonyms    []string     `json:"synonyms"`
+	Images      []FruitImage `json:"images"`
+	CreatedAt   time.Time    `json:"created_at"`
+	UpdatedAt   time.Time    `json:"updated_at"`
+}
+
+type FruitImage struct {
+	ID        int       `json:"id"`
+	FruitID   int       `json:"fruit_id"`
+	Filename  *string   `json:"filename"`
+	ImageType string    `json:"image_type"`
+	Title     *string   `json:"title"`
+	URL       string    `json:"url"`
+	CreatedAt time.Time `json:"created_at"`
+}
+
+type FruitWriteDTO struct {
+	Name       string   `json:"name"`
+	OSDBNumber string   `json:"osdb_number"`
+	Comment    *string  `json:"comment"`
+	FruitType  string   `json:"fruit_type"`
+	Synonyms   []string `json:"synonyms"`
+}
+
+type FruitListResponse struct {
+	Items  []Fruit `json:"items"`
+	Total  int     `json:"total"`
+	Limit  int     `json:"limit"`
+	Offset int     `json:"offset"`
+}