refactor(cards): collections JSON detail + preview-adjacent ladder through the builder

GET /api/collections/:id books — all four branches now build cards via
the cards.go adapters. LibraryTypeMap hoisted to once per handler (it
was 1 query per item in the smart and no-library branches). The system
branch — which before stamped cards BARE (no format_group, no badge —
the ladder's only JSON gap) — now emits the same card shape as its
siblings by feeding section.Items through BookCardsFromMediaItems,
matching what BuildSections produces for the identical data. The
collection-error seed dies via the adapters' non-nil empty slices;
the no-matching-section nil result is preserved as-is (that branch
never seeded — today's 'items': null stays today's 'items': null).

Pins: CollectionsJSON, DashboardSections, MediaListBothBranches green.

internal/handlers/collections.go

@@ -254,6 +254,7 @@ func (h *CollectionHandler) GetCollection(c *echo.Context) error {
 	}
 
 	isSmart := h.collectionService.IsSmartCollection(collection.AutoAssignRules)
+	libTypes := LibraryTypeMap(c.Request().Context(), h.db)
 	if isSmart {
 		rules := h.collectionService.ParseRules(collection.AutoAssignRules)
 		visibleIDs, err := h.userVisibleLibraryIDs(c)
@@ -267,19 +268,7 @@ func (h *CollectionHandler) GetCollection(c *echo.Context) error {
 		if evalErr != nil {
 			return c.JSON(http.StatusInternalServerError, map[string]string{"error": evalErr.Error()})
 		}
-		bookList = make([]BookInfo, 0, len(matches))
+		bookList = BookCardsFromMediaItems(matches, libTypes)
-		for _, item := range matches {
-			itemUUID, _ := uuid.FromBytes(item.ID.Bytes[0:16])
-			libTypes := LibraryTypeMap(c.Request().Context(), h.db)
-			bookList = append(bookList, BookInfo{
-				MediaItemID:    itemUUID.String(),
-				Title:          item.Title,
-				Author:         textToString(item.Author),
-				CoverImagePath: utils.ResolveMediaURL(item.LibraryID, item.CoverImagePath),
-				FormatGroup:    item.FormatGroup,
-				Badge:          MediaBadgeKind(item.FormatGroup, libTypes[uuid.UUID(item.LibraryID.Bytes).String()]),
-			})
-		}
 	} else if collection.IsSystemCollection.Bool && collection.QueryType.Valid && collection.QueryType.String != "" && collection.QueryType.String != "filter" {
 		user := c.Get("user").(database.Users)
 		userUUID := uuid.UUID(user.ID.Bytes)
@@ -290,17 +279,7 @@ func (h *CollectionHandler) GetCollection(c *echo.Context) error {
 		}
 		for _, section := range sections {
 			if section.CollectionID == collectionID {
-				bookCards := make([]BookInfo, len(section.Items))
+				bookList = BookCardsFromMediaItems(section.Items, libTypes)
-				for i, item := range section.Items {
-					itemUUID, _ := uuid.FromBytes(item.ID.Bytes[0:16])
-					bookCards[i] = BookInfo{
-						MediaItemID:    itemUUID.String(),
-						Title:          item.Title,
-						Author:         textToString(item.Author),
-						CoverImagePath: utils.ResolveMediaURL(item.LibraryID, item.CoverImagePath),
-					}
-				}
-				bookList = bookCards
 				break
 			}
 		}
@@ -312,7 +291,7 @@ func (h *CollectionHandler) GetCollection(c *echo.Context) error {
 				Limit:        pgtype.Int4{Int32: 10000, Valid: true},
 			})
 		if collErr != nil {
-			bookList = []BookInfo{}
+			bookList = BookCardsFromCollectionDashRows(nil, libTypes)
 		} else {
 			var validItems []database.GetCollectionItemsForDashboardRow
 			for _, item := range collItems {
@@ -320,38 +299,14 @@ func (h *CollectionHandler) GetCollection(c *echo.Context) error {
 					validItems = append(validItems, item)
 				}
 			}
-			libTypes := LibraryTypeMap(c.Request().Context(), h.db)
+			bookList = BookCardsFromCollectionDashRows(validItems, libTypes)
-			bookCards := make([]BookInfo, len(validItems))
-			for i, item := range validItems {
-				itemUUID, _ := uuid.FromBytes(item.ID.Bytes[0:16])
-				bookCards[i] = BookInfo{
-					MediaItemID:    itemUUID.String(),
-					Title:          item.Title,
-					Author:         textToString(item.Author),
-					CoverImagePath: utils.ResolveMediaURL(item.LibraryID, item.CoverImagePath),
-					FormatGroup:    item.FormatGroup,
-					Badge:          MediaBadgeKind(item.FormatGroup, libTypes[uuid.UUID(item.LibraryID.Bytes).String()]),
-				}
-			}
-			bookList = bookCards
 		}
 	} else {
 		books, booksErr := h.GetCollectionBooksData(c, collectionID)
 		if booksErr != nil {
 			return c.JSON(http.StatusInternalServerError, map[string]string{"error": booksErr.Error()})
 		}
-		bookList = make([]BookInfo, 0, len(books))
+		bookList = BookCardsFromCollectionItemRows(books, libTypes)
-		for _, book := range books {
-			libTypes := LibraryTypeMap(c.Request().Context(), h.db)
-			bookList = append(bookList, BookInfo{
-				MediaItemID:    uuid.UUID(book.MediaItemID.Bytes).String(),
-				Title:          book.Title,
-				Author:         textToString(book.Author),
-				CoverImagePath: utils.ResolveMediaURL(book.LibraryID, book.CoverImagePath),
-				FormatGroup:    book.FormatGroup,
-				Badge:          MediaBadgeKind(book.FormatGroup, libTypes[uuid.UUID(book.LibraryID.Bytes).String()]),
-			})
-		}
 	}
 
 	var viewSettings map[string]interface{}