feat: add Pydantic schemas for AI fix-tree endpoint

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

backend/app/schemas/ai_fix.py

@@ -0,0 +1,52 @@
+"""Pydantic schemas for the AI auto-fix feature."""
+from typing import Any, Literal
+
+from pydantic import BaseModel, Field
+
+
+# ── Requests ──
+
+
+class ValidationErrorInput(BaseModel):
+    """A single validation error to fix."""
+
+    node_id: str = Field(..., description="ID of the node with the error")
+    message: str = Field(..., description="The validation error message")
+
+
+class AIFixTreeRequest(BaseModel):
+    """Request to generate AI fixes for validation errors."""
+
+    tree_structure: dict[str, Any] = Field(..., description="Full tree structure")
+    tree_name: str = Field("", max_length=255, description="Name of the flow")
+    tree_type: Literal["troubleshooting", "procedural", "maintenance"] = Field(
+        "troubleshooting", description="Type of flow"
+    )
+    validation_errors: list[ValidationErrorInput] = Field(
+        ..., min_length=1, max_length=10, description="Errors to fix"
+    )
+
+
+# ── Responses ──
+
+
+class AIFixProposal(BaseModel):
+    """A single proposed fix from the AI."""
+
+    target_node_id: str
+    error_message: str
+    description: str
+    original_node: dict[str, Any]
+    fixed_node: dict[str, Any]
+
+
+class AIFixTokenUsage(BaseModel):
+    input: int = 0
+    output: int = 0
+
+
+class AIFixTreeResponse(BaseModel):
+    """Response with proposed fixes."""
+
+    fixes: list[AIFixProposal]
+    tokens_used: AIFixTokenUsage