feat: add delete schoolyear route and handler

backend/handlers.go

@@ -690,3 +690,26 @@ func (app *App) GenerateYearlySummaryPDFHandler(c echo.Context) error {
 
 	return c.Blob(http.StatusOK, "application/pdf", pdfBytes)
 }
+
+func (app *App) DeleteSchoolYearHandler(c echo.Context) error {
+	id, err := strconv.Atoi(c.Param("id"))
+	if err != nil {
+		return HandleError(c, ErrInvalidInputMsg("Schuljahr-ID"))
+	}
+
+	if err := DeleteSchoolYear(app.DB, id); err != nil {
+		if err == sql.ErrNoRows {
+			return HandleError(c, ErrNotFoundMsg("Schuljahr"))
+		}
+		if err.Error() == "cannot delete active school year" {
+			return HandleError(c, &AppError{
+				Code:       "CANNOT_DELETE_ACTIVE_SCHOOL_YEAR",
+				Message:    "Aktives Schuljahr kann nicht gelöscht werden",
+				HTTPStatus: http.StatusBadRequest,
+			})
+		}
+		return HandleError(c, ErrDatabaseMsg(err))
+	}
+
+	return c.NoContent(http.StatusNoContent)
+}