feat(core): add Currency model

app/models/currency.py

@@ -0,0 +1,31 @@
+"""Currency model — multi-currency support for ERP."""
+
+from __future__ import annotations
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import Boolean, DateTime, Index, String
+from sqlalchemy.dialects.postgresql import UUID as PGUUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.core.db import Base, TenantMixin
+
+
+class Currency(Base, TenantMixin):
+    """Currency entity — e.g. EUR, USD, GBP."""
+
+    __tablename__ = "currencies"
+    __table_args__ = (
+        Index("ix_currencies_tenant_code", "tenant_id", "code"),
+        Index("ix_currencies_tenant_default", "tenant_id", "is_default"),
+    )
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        PGUUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    code: Mapped[str] = mapped_column(String(3), nullable=False, unique=True)
+    name: Mapped[str] = mapped_column(String(50), nullable=False)
+    symbol: Mapped[str] = mapped_column(String(5), nullable=False)
+    is_default: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
+    deleted_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)