feat: add User registration infrastructure layer

[zigzagdev]

Motivation

The application needs a persistence layer for the User domain. Without a repository, there is no way to create users from the application layer.
This PR introduces the infrastructure layer that bridges the UserEntity domain object and the Eloquent User model, providing a clean boundary between domain logic and database concerns.

What I have done

• Added UserRepositoryInterface to define the contract for user persistence
• Added UserRepository implementing the interface with Eloquent, mapping UserEntity fields (email, first_name, last_name, age_range, subscription_tier, subscription_expires_at) to the fillable columns and using wasRecentlyCreated to detect insert failures
• Added UserDto as a stub returned by createUser (full implementation deferred to next branch)
• Fixed SubscriptionFactory namespace mismatch — the file lived under Factory/ but declared namespace Subscription; corrected to Factory and added missing use statements for Subscription and SubscriptionTier
• Updated UserEntityFactory import to match the corrected SubscriptionFactory namespace
• Added unit tests using Mockery (to mock the static Model::create()) and Faker (to generate randomised, non-duplicate test data)

Test Results

PASS  Tests\Unit\Packages\Domains\UserRepositoryTest
✓ create user returns user dto on success
✓ create user throws exception when insert fails

Tests: 2 passed (3 assertions)

[zigzagdev]

Ok