feat: add AI suggestion audit trail table

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

backend/alembic/env.py

@@ -16,6 +16,7 @@ from app.models.copilot_conversation import CopilotConversation
 from app.models.assistant_chat import AssistantChat
 from app.models.survey_response import SurveyResponse
 from app.models.survey_invite import SurveyInvite
+from app.models.ai_suggestion import AISuggestion  # noqa: F401
 from app.core.config import settings
 
 # this is the Alembic Config object

backend/alembic/versions/052_add_ai_suggestion_table.py

@@ -0,0 +1,37 @@
+"""add ai suggestion table
+
+Revision ID: 052
+Revises: 051
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+
+revision = "052"
+down_revision = "051"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "ai_suggestions",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True),
+        sa.Column("tree_id", UUID(as_uuid=True), sa.ForeignKey("trees.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("user_id", UUID(as_uuid=True), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("session_id", UUID(as_uuid=True), sa.ForeignKey("ai_chat_sessions.id", ondelete="SET NULL"), nullable=True),
+        sa.Column("action_type", sa.String(50), nullable=False),
+        sa.Column("target_node_id", sa.String(255), nullable=True),
+        sa.Column("changes_json", JSONB, nullable=False, server_default="{}"),
+        sa.Column("status", sa.String(20), nullable=False, server_default="pending"),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.Column("resolved_at", sa.DateTime(timezone=True), nullable=True),
+    )
+    op.create_index("ix_ai_suggestions_tree_id", "ai_suggestions", ["tree_id"])
+    op.create_index("ix_ai_suggestions_user_id", "ai_suggestions", ["user_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_ai_suggestions_user_id", table_name="ai_suggestions")
+    op.drop_index("ix_ai_suggestions_tree_id", table_name="ai_suggestions")
+    op.drop_table("ai_suggestions")