Plant catalog backend: CRUD + seeded built-ins (#12)

Co-authored-by: Steve Dudenhoeffer <[email protected]>

internal/store/users.go

@@ -177,3 +177,10 @@ func boolToInt(b bool) int {
 func isUniqueViolation(err error) bool {
 	return err != nil && strings.Contains(err.Error(), "UNIQUE constraint failed")
 }
+
+// isForeignKeyViolation reports whether err is a SQLite FOREIGN KEY-constraint
+// failure — e.g. deleting a plant a planting still references (ON DELETE
+// RESTRICT). Same stable-message approach as isUniqueViolation.
+func isForeignKeyViolation(err error) bool {
+	return err != nil && strings.Contains(err.Error(), "FOREIGN KEY constraint failed")
+}