feat: add next_steps column and update session schemas

- Add next_steps TEXT column to sessions table via migration 034
- Add include_outcome_notes, include_next_steps, max_step_index to SessionExport
- Add next_steps to SessionUpdate, SessionResponse, SessionComplete

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/alembic/versions/034_add_next_steps_to_sessions.py

@@ -0,0 +1,27 @@
+"""add next_steps to sessions
+
+Revision ID: 034
+Revises: 033
+Create Date: 2026-02-13
+
+Adds next_steps TEXT column to sessions table.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '034'
+down_revision: Union[str, None] = '033'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column('sessions', sa.Column('next_steps', sa.Text(), server_default=sa.text("''"), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column('sessions', 'next_steps')