feat(evidence): add S3 storage service and file_uploads model

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -47,6 +47,7 @@ from .notification_config import NotificationConfig
 from .notification_log import NotificationLog
 from .notification import Notification
 from .psa_activity_log import PsaActivityLog
+from .file_upload import FileUpload
 
 __all__ = [
     "User",
@@ -108,4 +109,5 @@ __all__ = [
     "NotificationLog",
     "Notification",
     "PsaActivityLog",
+    "FileUpload",
 ]

backend/app/models/file_upload.py

@@ -0,0 +1,32 @@
+"""File upload metadata — tracks files stored in S3-compatible object storage."""
+import uuid
+from datetime import datetime, timezone
+from typing import Optional
+
+from sqlalchemy import String, Integer, DateTime, ForeignKey
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.dialects.postgresql import UUID
+
+from app.core.database import Base
+
+
+class FileUpload(Base):
+    __tablename__ = "file_uploads"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    account_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("accounts.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    uploaded_by: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=False
+    )
+    session_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("ai_sessions.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    filename: Mapped[str] = mapped_column(String(255), nullable=False)
+    content_type: Mapped[str] = mapped_column(String(100), nullable=False)
+    size_bytes: Mapped[int] = mapped_column(Integer, nullable=False)
+    storage_key: Mapped[str] = mapped_column(String(500), nullable=False, unique=True)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )