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/schemas/__init__.py

@@ -0,0 +1,17 @@
+from app.schemas.auth import (
+    LoginRequest,
+    LoginResponse,
+    TokenResponse,
+    RefreshRequest,
+    UserResponse,
+    CreateUserRequest,
+)
+
+__all__ = [
+    "LoginRequest",
+    "LoginResponse",
+    "TokenResponse",
+    "RefreshRequest",
+    "UserResponse",
+    "CreateUserRequest",
+]