feat(FN-2724): add interactive task routing controls

- Replace the static routing panel with a dedicated Routing tab that shows effective node, source, and policy details
- Add per-task node override selection with optimistic save/rollback, clear override action, and in-progress lock messaging
- Tighten PATCH /tasks/:id nodeId validation (empty/non-string rejection) while preserving node override conflict enforcement
- Update dashboard route and modal tests, including new RoutingTab coverage and tab-order assertions

packages/dashboard/app/api/legacy.ts

@@ -298,6 +298,7 @@ export function updateTask(
     executionMode?: "standard" | "fast" | null;
     priority?: TaskPriority | null;
     sourceIssue?: TaskSourceIssue | null;
+    nodeId?: string | null;
   },
   projectId?: string,
 ): Promise<Task> {