feat(FN-4966): complete Step 4 — wire diagnostics into PR refresh routes

Fusion-Task-Id: FN-4966
Fusion-Task-Lineage: 8f5ea300-feaa-469c-aeed-f7304a5a1b6d

packages/dashboard/app/api/legacy.ts

@@ -65,6 +65,7 @@ import type {
   ResearchRunStatus,
   TaskPriority,
   TaskSourceIssue,
+  PrConflictDiagnostics,
   PrInfo,
   ManagedDockerNodeInput,
   DockerNodeConfig,
@@ -2199,6 +2200,7 @@ export interface PrStatusResponse {
 
 export interface PrRefreshResponse {
   prInfo: PrInfo;
+  conflictDiagnostics?: PrConflictDiagnostics;
   mergeReady: boolean;
   mergeable?: PrInfo["mergeable"];
   blockingReasons: string[];