feat(ebooks): add ISBN normalization and graceful library requirement handling

- Increase ISBN column from VARCHAR(13) to VARCHAR(17) to support ISBN-13 with hyphens
- Add normalize_isbn() database function to automatically remove hyphens and spaces
- Create trigger to auto-normalize ISBNs on INSERT/UPDATE operations
- Update all Ebook and MediaItem queries to use ISBN normalization
- Add GetEbookLibraryID query to check for existing ebook libraries
- Add graceful error handling when no ebook library exists
- Return helpful error message: 'no ebook library found. Please create an ebook library first'
- Create comprehensive tests for ISBN normalization and library selection
- Add Bruno test files for various ISBN formats and error scenarios
- Update documentation with ISBN normalization details

internal/handlers/ebook.go

@@ -232,6 +232,17 @@ func (h *Handler) CreateEbook(c echo.Context) error {
 		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid user id"})
 	}
 
+	// Check if an ebook library exists before attempting to create an ebook
+	_, err = h.db.GetEbookLibraryID(c.Request().Context())
+	if err != nil {
+		if err == pgx.ErrNoRows {
+			return c.JSON(http.StatusBadRequest, map[string]string{
+				"error": "no ebook library found. Please create an ebook library first",
+			})
+		}
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
+	}
+
 	ebook, err := h.db.CreateEbook(c.Request().Context(), database.CreateEbookParams{
 		Title:          req.Title,
 		Author:         pgtype.Text{String: req.Author, Valid: req.Author != ""},