Database support

Added connection
Added healthcheck
Added migration

backend/db/migrations.sql

@@ -0,0 +1,8 @@
+-- Create users table if it doesn't exist
+CREATE TABLE IF NOT EXISTS users (
+    id INT PRIMARY KEY,
+    username TEXT NOT NULL UNIQUE,
+    password TEXT NOT NULL,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+