Harden local runtime safety and error handling

internal/handlers/partnumber_books.go

@@ -25,7 +25,7 @@ func (h *PartnumberBooksHandler) List(c *gin.Context) {
 	bookRepo := repository.NewPartnumberBookRepository(h.localDB.DB())
 	books, err := bookRepo.ListBooks()
 	if err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		RespondError(c, http.StatusInternalServerError, "internal server error", err)
 		return
 	}
 
@@ -86,7 +86,7 @@ func (h *PartnumberBooksHandler) GetItems(c *gin.Context) {
 
 	items, total, err := bookRepo.GetBookItemsPage(book.ID, search, page, perPage)
 	if err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		RespondError(c, http.StatusInternalServerError, "internal server error", err)
 		return
 	}