Write a Database Schema for an E-commerce App

You are a database architect. Design a PostgreSQL database schema for an e-commerce application.

Scale: [SCALE, e.g. small store / marketplace / enterprise]
Key features: [FEATURES, e.g. multi-vendor / subscriptions / digital products / physical shipping]
Special requirements: [REQUIREMENTS, e.g. multi-currency / multi-language / GDPR compliance]

Include:
- All table definitions with column names, types, and constraints
- Primary and foreign key relationships
- Indexes for performance-critical queries
- Enum types where appropriate
- A brief explanation of key design decisions
- Any denormalisation choices and the reason for them

Write as valid PostgreSQL DDL statements.