feat(phase-1): Complete foundation setup

- Add User model and authentication system with JWT cookies
- Implement login/logout routes and protected dashboard
- Add Alembic database migration configuration
- Add create_admin.py script for initial user setup
- Make ContentGenerator and ImageGenerator lazy-initialized
- Add comprehensive API keys setup documentation
- Fix startup errors when services unavailable

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/models/__init__.py

@@ -4,6 +4,7 @@ Modelos de base de datos SQLAlchemy.
 
 from app.core.database import Base
 
+from app.models.user import User
 from app.models.product import Product
 from app.models.service import Service
 from app.models.tip_template import TipTemplate
@@ -14,6 +15,7 @@ from app.models.interaction import Interaction
 
 __all__ = [
     "Base",
+    "User",
     "Product",
     "Service",
     "TipTemplate",