feat: add user entity and role model

src/main/java/com/slotline/user/Role.java

@@ -0,0 +1,6 @@
+package com.slotline.user;
+
+public enum Role {
+    USER,
+    ADMIN
+}

src/main/java/com/slotline/user/User.java

@@ -0,0 +1,72 @@
+package com.slotline.user;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.EnumType;
+import jakarta.persistence.Enumerated;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.Table;
+
+import java.time.Instant;
+
+@Entity
+@Table(name = "app_user")
+public class User {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @Column(name = "organization_id", nullable = false)
+    private Long organizationId;
+
+    @Column(nullable = false, unique = true, length = 64)
+    private String username;
+
+    @Column(name = "password_hash", nullable = false, length = 100)
+    private String passwordHash;
+
+    @Enumerated(EnumType.STRING)
+    @Column(nullable = false, length = 16)
+    private Role role;
+
+    @Column(name = "created_at", nullable = false)
+    private Instant createdAt;
+
+    protected User() {
+    }
+
+    public User(Long organizationId, String username, String passwordHash, Role role, Instant createdAt) {
+        this.organizationId = organizationId;
+        this.username = username;
+        this.passwordHash = passwordHash;
+        this.role = role;
+        this.createdAt = createdAt;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public Long getOrganizationId() {
+        return organizationId;
+    }
+
+    public String getUsername() {
+        return username;
+    }
+
+    public String getPasswordHash() {
+        return passwordHash;
+    }
+
+    public Role getRole() {
+        return role;
+    }
+
+    public Instant getCreatedAt() {
+        return createdAt;
+    }
+}

src/main/java/com/slotline/user/UserRepository.java

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+package com.slotline.user;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.Optional;
+
+public interface UserRepository extends JpaRepository<User, Long> {
+
+    Optional<User> findByUsername(String username);
+
+    boolean existsByUsername(String username);
+}