feat(core): add Attachment model

app/models/attachment.py

@@ -0,0 +1,35 @@
+"""Attachment model — file attachments for any entity."""
+
+from __future__ import annotations
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, Index, Integer, String
+from sqlalchemy.dialects.postgresql import UUID as PGUUID
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.core.db import Base, TenantMixin
+
+
+class Attachment(Base, TenantMixin):
+    """Attachment entity — links files to companies, contacts, invoices, etc."""
+
+    __tablename__ = "attachments"
+    __table_args__ = (
+        Index("ix_attachments_entity", "entity_type", "entity_id", "tenant_id"),
+    )
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        PGUUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    entity_type: Mapped[str] = mapped_column(String(50), nullable=False)
+    entity_id: Mapped[uuid.UUID] = mapped_column(PGUUID(as_uuid=True), nullable=False)
+    filename: Mapped[str] = mapped_column(String(255), nullable=False)
+    file_path: Mapped[str] = mapped_column(String(500), nullable=False)
+    mime_type: Mapped[str] = mapped_column(String(100), nullable=False, default="application/octet-stream")
+    file_size: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+    uploaded_by: Mapped[uuid.UUID | None] = mapped_column(
+        PGUUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=True
+    )
+    deleted_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)