feat: add Layer 2 - WhatsApp Core logic, API Gateway models/auth, Frontend core

WhatsApp Core:
- SessionManager with Baileys integration for multi-account support
- Express server with REST API and Socket.IO for real-time events
- Session lifecycle management (create, disconnect, delete)
- Message sending with support for text, image, document, audio, video

API Gateway:
- Database models: User, WhatsAppAccount, Contact, Conversation, Message
- JWT authentication with access/refresh tokens
- Auth endpoints: login, refresh, register, me
- Pydantic schemas for request/response validation

Frontend:
- React 18 app structure with routing
- Zustand auth store with persistence
- API client with automatic token handling
- Base CSS and TypeScript declarations

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

services/api-gateway/app/models/user.py

@@ -0,0 +1,33 @@
+import uuid
+from datetime import datetime
+from sqlalchemy import Column, String, Boolean, DateTime, Enum as SQLEnum
+from sqlalchemy.dialects.postgresql import UUID
+import enum
+from app.core.database import Base
+
+
+class UserRole(str, enum.Enum):
+    ADMIN = "admin"
+    SUPERVISOR = "supervisor"
+    AGENT = "agent"
+
+
+class UserStatus(str, enum.Enum):
+    ONLINE = "online"
+    OFFLINE = "offline"
+    AWAY = "away"
+    BUSY = "busy"
+
+
+class User(Base):
+    __tablename__ = "users"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    email = Column(String(255), unique=True, nullable=False, index=True)
+    password_hash = Column(String(255), nullable=False)
+    name = Column(String(100), nullable=False)
+    role = Column(SQLEnum(UserRole), default=UserRole.AGENT, nullable=False)
+    status = Column(SQLEnum(UserStatus), default=UserStatus.OFFLINE, nullable=False)
+    is_active = Column(Boolean, default=True, nullable=False)
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow, nullable=False)