feat: add AI suggestion audit trail endpoints

Create/list/resolve endpoints for tracking AI-applied changes to flows.

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

backend/app/schemas/ai_suggestion.py

@@ -0,0 +1,33 @@
+"""Schemas for AI suggestion audit trail."""
+from datetime import datetime
+from typing import Optional
+from uuid import UUID
+
+from pydantic import BaseModel, Field
+
+
+class AISuggestionCreate(BaseModel):
+    tree_id: UUID
+    session_id: Optional[UUID] = None
+    action_type: str
+    target_node_id: Optional[str] = None
+    changes_json: dict = Field(default_factory=dict)
+
+
+class AISuggestionResponse(BaseModel):
+    id: UUID
+    tree_id: UUID
+    user_id: UUID
+    session_id: Optional[UUID]
+    action_type: str
+    target_node_id: Optional[str]
+    changes_json: dict
+    status: str
+    created_at: datetime
+    resolved_at: Optional[datetime]
+
+    model_config = {"from_attributes": True}
+
+
+class AISuggestionResolve(BaseModel):
+    status: str = Field(..., pattern="^(accepted|dismissed)$")