fix: update SQL queries to use parameterized table names for security

Co-authored-by: Copilot <copilot@github.com>

backend/scheme.sql

@@ -6,6 +6,7 @@ CREATE TABLE users (
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
 );
 
+/* This scheme does not have to be implemented manually. It always will be generated by the backend */
 CREATE TABLE xx_DD_MM_YYYY (
     id INT AUTO_INCREMENT PRIMARY KEY,
     Vorname VARCHAR(100) NOT NULL,