Harden reconciliation conflict handling

api/schemas/reconciliation.py

@@ -15,6 +15,7 @@ class StateChangeRequest(BaseModel):
     target_status: str
     actor: str = "dashboard"
     intent: str | None = None
+    expected_current_status: str | None = None
     file_backed: bool | None = None
     archived_file: bool | None = None
     task_linked: bool | None = None
@@ -40,3 +41,4 @@ class StateChangeResponse(BaseModel):
     write_through_result: Literal["not_attempted", "applied", "not_applicable"] = "not_attempted"
     workplan_path: str | None = None
     reconciliation_record_id: uuid.UUID | None = None
+    conflict: bool = False