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

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

backend/alembic/versions/49150866ae44_add_file_uploads_table.py

@@ -0,0 +1,46 @@
+"""add file_uploads table
+
+Revision ID: 49150866ae44
+Revises: e0d382f083d4
+Create Date: 2026-03-20 03:15:10.227797
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '49150866ae44'
+down_revision: Union[str, None] = 'e0d382f083d4'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        'file_uploads',
+        sa.Column('id', sa.UUID(), nullable=False),
+        sa.Column('account_id', sa.UUID(), nullable=False),
+        sa.Column('uploaded_by', sa.UUID(), nullable=False),
+        sa.Column('session_id', sa.UUID(), nullable=True),
+        sa.Column('filename', sa.String(length=255), nullable=False),
+        sa.Column('content_type', sa.String(length=100), nullable=False),
+        sa.Column('size_bytes', sa.Integer(), nullable=False),
+        sa.Column('storage_key', sa.String(length=500), nullable=False),
+        sa.Column('created_at', sa.DateTime(timezone=True), nullable=False),
+        sa.ForeignKeyConstraint(['account_id'], ['accounts.id'], ondelete='CASCADE'),
+        sa.ForeignKeyConstraint(['session_id'], ['ai_sessions.id'], ondelete='SET NULL'),
+        sa.ForeignKeyConstraint(['uploaded_by'], ['users.id'], ondelete='SET NULL'),
+        sa.PrimaryKeyConstraint('id'),
+        sa.UniqueConstraint('storage_key'),
+    )
+    op.create_index(op.f('ix_file_uploads_account_id'), 'file_uploads', ['account_id'], unique=False)
+    op.create_index(op.f('ix_file_uploads_session_id'), 'file_uploads', ['session_id'], unique=False)
+
+
+def downgrade() -> None:
+    op.drop_index(op.f('ix_file_uploads_session_id'), table_name='file_uploads')
+    op.drop_index(op.f('ix_file_uploads_account_id'), table_name='file_uploads')
+    op.drop_table('file_uploads')