feat: implement MainForm component and set up routing; add user table schema and trigger in SQL

backend/scheme.sql

@@ -0,0 +1,24 @@
+CREATE TABLE users (
+    id INT AUTO_INCREMENT PRIMARY KEY,
+    username VARCHAR(100) NOT NULL,
+    first_name VARCHAR(100) NOT NULL,
+    last_name VARCHAR(100) NOT NULL,
+    email VARCHAR(255) NOT NULL UNIQUE,
+    unique_key CHAR(25) NOT NULL UNIQUE,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Trigger zur automatischen Generierung eines 25‑stelligen Keys
+DELIMITER $
+
+CREATE TRIGGER before_user_insert
+BEFORE INSERT ON users
+FOR EACH ROW
+BEGIN
+    SET NEW.unique_key = SUBSTRING(
+        REPLACE(UUID(), '-', '')
+        -- UUID = 32 Zeichen, wir nehmen 25 davon
+    , 1, 25);
+END$
+
+DELIMITER ;