refactor: migrate modules from re-exports to canonical implementations

Move actual code implementations into module directories:
- orders: 5 services, 4 models, order/invoice schemas
- inventory: 3 services, 2 models, 30+ schemas
- customers: 3 services, 2 models, customer schemas
- messaging: 3 services, 2 models, message/notification schemas
- monitoring: background_tasks_service
- marketplace: 5+ services including letzshop submodule
- dev_tools: code_quality_service, test_runner_service
- billing: billing_service
- contracts: definition.py

Legacy files in app/services/, models/database/, models/schema/
now re-export from canonical module locations for backwards
compatibility. Architecture validator passes with 0 errors.

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

app/modules/customers/models/customer.py

@@ -0,0 +1,93 @@
+# app/modules/customers/models/customer.py
+"""
+Customer database models.
+
+Provides Customer and CustomerAddress models for vendor-scoped
+customer management.
+"""
+
+from sqlalchemy import (
+    JSON,
+    Boolean,
+    Column,
+    DateTime,
+    ForeignKey,
+    Integer,
+    Numeric,
+    String,
+)
+from sqlalchemy.orm import relationship
+
+from app.core.database import Base
+from models.database.base import TimestampMixin
+
+
+class Customer(Base, TimestampMixin):
+    """Customer model with vendor isolation."""
+
+    __tablename__ = "customers"
+
+    id = Column(Integer, primary_key=True, index=True)
+    vendor_id = Column(Integer, ForeignKey("vendors.id"), nullable=False)
+    email = Column(
+        String(255), nullable=False, index=True
+    )  # Unique within vendor scope
+    hashed_password = Column(String(255), nullable=False)
+    first_name = Column(String(100))
+    last_name = Column(String(100))
+    phone = Column(String(50))
+    customer_number = Column(
+        String(100), nullable=False, index=True
+    )  # Vendor-specific ID
+    preferences = Column(JSON, default=dict)
+    marketing_consent = Column(Boolean, default=False)
+    last_order_date = Column(DateTime)
+    total_orders = Column(Integer, default=0)
+    total_spent = Column(Numeric(10, 2), default=0)
+    is_active = Column(Boolean, default=True, nullable=False)
+
+    # Language preference (NULL = use vendor storefront_language default)
+    # Supported: en, fr, de, lb
+    preferred_language = Column(String(5), nullable=True)
+
+    # Relationships
+    vendor = relationship("Vendor", back_populates="customers")
+    addresses = relationship("CustomerAddress", back_populates="customer")
+    orders = relationship("Order", back_populates="customer")
+
+    def __repr__(self):
+        return f"<Customer(id={self.id}, vendor_id={self.vendor_id}, email='{self.email}')>"
+
+    @property
+    def full_name(self):
+        if self.first_name and self.last_name:
+            return f"{self.first_name} {self.last_name}"
+        return self.email
+
+
+class CustomerAddress(Base, TimestampMixin):
+    """Customer address model for shipping and billing addresses."""
+
+    __tablename__ = "customer_addresses"
+
+    id = Column(Integer, primary_key=True, index=True)
+    vendor_id = Column(Integer, ForeignKey("vendors.id"), nullable=False)
+    customer_id = Column(Integer, ForeignKey("customers.id"), nullable=False)
+    address_type = Column(String(50), nullable=False)  # 'billing', 'shipping'
+    first_name = Column(String(100), nullable=False)
+    last_name = Column(String(100), nullable=False)
+    company = Column(String(200))
+    address_line_1 = Column(String(255), nullable=False)
+    address_line_2 = Column(String(255))
+    city = Column(String(100), nullable=False)
+    postal_code = Column(String(20), nullable=False)
+    country_name = Column(String(100), nullable=False)
+    country_iso = Column(String(5), nullable=False)
+    is_default = Column(Boolean, default=False)
+
+    # Relationships
+    vendor = relationship("Vendor")
+    customer = relationship("Customer", back_populates="addresses")
+
+    def __repr__(self):
+        return f"<CustomerAddress(id={self.id}, customer_id={self.customer_id}, type='{self.address_type}')>"