refactor(cards): SSR series and tag pages through the builder

Both BrowseDetail surfaces hand-rolled bare 4-field literals (badges
dropped) and patched the nil-slice with []BookInfo{} seeds after.
BookCardsFromMediaItems feeds GetSeriesBooks/GetBooksByTag rows —
cards gain format_group + badge on the series and tag pages, and the
two seed blocks die with the adapter's non-nil empties. Conflict
stamping at these sites was already adjacent and is preserved.

internal/router/frontend.go

@@ -241,20 +241,7 @@ func registerFrontendRoutes(cfg *Config) {
 			log.Printf("GetSeriesBooks failed: %v", err)
 			errorMsg = "Error loading series books"
 		} else {
-			bookInfoList = make([]handlers.BookInfo, 0, len(books))
+			bookInfoList = handlers.BookCardsFromMediaItems(books, handlers.LibraryTypeMap(c.Request().Context(), cfg.Queries))
-			for _, item := range books {
-				itemUUID, _ := uuid.FromBytes(item.ID.Bytes[0:16])
-				bookInfoList = append(bookInfoList, handlers.BookInfo{
-					MediaItemID:    itemUUID.String(),
-					Title:          item.Title,
-					Author:         textToString(item.Author),
-					CoverImagePath: utils.ResolveMediaURL(item.LibraryID, item.CoverImagePath),
-				})
-			}
-		}
-
-		if bookInfoList == nil {
-			bookInfoList = []handlers.BookInfo{}
 		}
 
 		seriesUserUUID, _ := uuid.Parse(user.ID)
@@ -295,22 +282,9 @@ func registerFrontendRoutes(cfg *Config) {
 				log.Printf("GetBooksByTag failed: %v", err)
 				errorMsg = "Error loading tag books"
 			} else {
-				bookInfoList = make([]handlers.BookInfo, 0, len(books))
+				bookInfoList = handlers.BookCardsFromMediaItems(books, handlers.LibraryTypeMap(c.Request().Context(), cfg.Queries))
-				for _, item := range books {
-					itemUUID, _ := uuid.FromBytes(item.ID.Bytes[0:16])
-					bookInfoList = append(bookInfoList, handlers.BookInfo{
-						MediaItemID:    itemUUID.String(),
-						Title:          item.Title,
-						Author:         textToString(item.Author),
-						CoverImagePath: utils.ResolveMediaURL(item.LibraryID, item.CoverImagePath),
-					})
 			}
 		}
-		}
-
-		if bookInfoList == nil {
-			bookInfoList = []handlers.BookInfo{}
-		}
 
 		tagUserUUID, _ := uuid.Parse(user.ID)
 		bookInfoList = handlers.MarkActiveConflicts(c.Request().Context(), cfg.Queries, pgtype.UUID{Bytes: tagUserUUID, Valid: true}, bookInfoList)