feat: fruit overview with thumbnails and card layout (story #07)

- Auto-crop thumbnails on image upload (Go stdlib, no external deps):
  find non-background bounding box, pad 5px, scale to ≤300px, encode JPEG
- Add thumbnail_data BYTEA column to fruit_images and publication_fruit_images
- New GET /api/v1/fruits/:id/images/:imageId/thumbnail endpoint (fallback to full data)
- New GET /api/v1/publications/:id/fruit-images/:imgId/thumbnail endpoint
- New POST /api/v1/admin/backfill-thumbnails to retroactively generate thumbnails
- ListFruits response now includes synonyms and thumbnail_url per fruit
- Replace FruitList table with responsive FruitCard grid (thumbnail + name + OSDB ID + type + synonyms)

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

backend/internal/handler/admin_handler.go

@@ -0,0 +1,44 @@
+package handler
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/labstack/echo/v4"
+)
+
+type FruitBackfiller interface {
+	BackfillThumbnails(ctx context.Context) (int, error)
+}
+
+type PubBackfiller interface {
+	BackfillThumbnails(ctx context.Context) (int, error)
+}
+
+type AdminHandler struct {
+	fruitRepo FruitBackfiller
+	pubRepo   PubBackfiller
+}
+
+func NewAdminHandler(fruitRepo FruitBackfiller, pubRepo PubBackfiller) *AdminHandler {
+	return &AdminHandler{fruitRepo: fruitRepo, pubRepo: pubRepo}
+}
+
+func (h *AdminHandler) BackfillThumbnails(c echo.Context) error {
+	ctx := c.Request().Context()
+
+	fruitCount, err := h.fruitRepo.BackfillThumbnails(ctx)
+	if err != nil {
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": "backfill failed: " + err.Error()})
+	}
+
+	pubCount, err := h.pubRepo.BackfillThumbnails(ctx)
+	if err != nil {
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": "backfill failed: " + err.Error()})
+	}
+
+	return c.JSON(http.StatusOK, map[string]int{
+		"fruit_images_processed":       fruitCount,
+		"pub_fruit_images_processed":   pubCount,
+	})
+}

backend/internal/handler/fruit_handler.go

@@ -29,6 +29,7 @@ type FruitRepository interface {
 	ListImages(ctx context.Context, fruitID int) ([]domain.FruitImage, error)
 	AddImage(ctx context.Context, fruitID int, filename *string, data []byte, imageType string, title *string) (domain.FruitImage, error)
 	GetImageData(ctx context.Context, fruitID, imageID int) ([]byte, error)
+	GetThumbnailData(ctx context.Context, fruitID, imageID int) ([]byte, error)
 	DeleteImage(ctx context.Context, fruitID, imageID int) error
 }
 
@@ -291,3 +292,20 @@ func (h *FruitHandler) DeleteImage(c echo.Context) error {
 	}
 	return c.NoContent(http.StatusNoContent)
 }
+
+func (h *FruitHandler) ServeThumbnail(c echo.Context) error {
+	fruitID, err := parseID(c, "id")
+	if err != nil {
+		return err
+	}
+	imageID, err := parseID(c, "imageId")
+	if err != nil {
+		return err
+	}
+	data, err := h.repo.GetThumbnailData(c.Request().Context(), fruitID, imageID)
+	if err != nil {
+		return mapRepoError(c, err)
+	}
+	contentType := http.DetectContentType(data)
+	return c.Blob(http.StatusOK, contentType, data)
+}

backend/internal/handler/fruit_handler_test.go

@@ -194,6 +194,14 @@ func (r *fakeRepo) GetImageData(_ context.Context, fruitID, imageID int) ([]byte
 	return r.imageData[imageID], nil
 }
 
+func (r *fakeRepo) GetThumbnailData(_ context.Context, fruitID, imageID int) ([]byte, error) {
+	img, ok := r.images[imageID]
+	if !ok || img.FruitID != fruitID {
+		return nil, handler.ErrNotFound
+	}
+	return r.imageData[imageID], nil
+}
+
 func (r *fakeRepo) DeleteImage(_ context.Context, fruitID, imageID int) error {
 	img, ok := r.images[imageID]
 	if !ok || img.FruitID != fruitID {

backend/internal/handler/publication_handler.go

@@ -42,6 +42,7 @@ type PublicationRepository interface {
 	ListFruitImages(ctx context.Context, pubID int) ([]domain.PublicationFruitImage, error)
 	AddFruitImage(ctx context.Context, pubID, fruitID int, filename *string, data []byte) (domain.PublicationFruitImage, error)
 	GetFruitImageData(ctx context.Context, pubID, imgID int) ([]byte, error)
+	GetFruitImageThumbnailData(ctx context.Context, pubID, imgID int) ([]byte, error)
 	DeleteFruitImage(ctx context.Context, pubID, imgID int) error
 
 	GetFruitDescriptions(ctx context.Context, fruitID int) ([]domain.PublicationDescription, error)
@@ -386,6 +387,23 @@ func (h *PublicationHandler) ServeFruitImage(c echo.Context) error {
 	return c.Blob(http.StatusOK, contentType, data)
 }
 
+func (h *PublicationHandler) ServeFruitImageThumbnail(c echo.Context) error {
+	pubID, err := parseID(c, "id")
+	if err != nil {
+		return err
+	}
+	imgID, err := parseID(c, "imgId")
+	if err != nil {
+		return err
+	}
+	data, err := h.repo.GetFruitImageThumbnailData(c.Request().Context(), pubID, imgID)
+	if err != nil {
+		return mapPubRepoError(c, err)
+	}
+	contentType := http.DetectContentType(data)
+	return c.Blob(http.StatusOK, contentType, data)
+}
+
 func (h *PublicationHandler) DeleteFruitImage(c echo.Context) error {
 	pubID, err := parseID(c, "id")
 	if err != nil {

backend/internal/handler/publication_handler_test.go

@@ -265,6 +265,14 @@ func (r *fakePubRepo) GetFruitImageData(_ context.Context, pubID, imgID int) ([]
 	return r.fruitImgData[imgID], nil
 }
 
+func (r *fakePubRepo) GetFruitImageThumbnailData(_ context.Context, pubID, imgID int) ([]byte, error) {
+	img, ok := r.fruitImages[imgID]
+	if !ok || img.PublicationID != pubID {
+		return nil, handler.ErrNotFound
+	}
+	return r.fruitImgData[imgID], nil
+}
+
 func (r *fakePubRepo) DeleteFruitImage(_ context.Context, pubID, imgID int) error {
 	img, ok := r.fruitImages[imgID]
 	if !ok || img.PublicationID != pubID {