fix signup route and add create users table migration

migrations/20260628175120_create_users_table.sql

@@ -0,0 +1,13 @@
+-- +goose Up
+CREATE TABLE IF NOT EXISTS users (
+    id SERIAL PRIMARY KEY,
+    username VARCHAR(50) NOT NULL UNIQUE,
+    email VARCHAR(100) NOT NULL UNIQUE,
+    password_hash VARCHAR(255) NOT NULL,
+    role VARCHAR(20) DEFAULT 'user' CHECK (role IN ('admin', 'author', 'organizer', 'user')),
+    is_active BOOLEAN DEFAULT TRUE,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- +goose Down
+DROP TABLE IF EXISTS users;