feat(FN-3716): add planning mode priority controls for task routes and subt

Adds per-subtask priority controls to planning mode with three implementation steps (route priority support, UI controls, and design-token polish), gates research tools behind an experimental feature flag with a new core infrastructure module, and introduces a WhatsApp chat plugin with discovery and

Fusion-Task-Id: FN-3716

packages/dashboard/app/api/legacy.ts

@@ -2657,6 +2657,7 @@ export interface SubtaskItem {
   title: string;
   description: string;
   suggestedSize: "S" | "M" | "L";
+  priority?: TaskPriority;
   dependsOn: string[];
 }
 
@@ -2928,6 +2929,7 @@ export function createTasksFromPlanning(
     title: string;
     description: string;
     suggestedSize: "S" | "M" | "L";
+    priority?: TaskPriority;
     dependsOn: string[];
   }>,
   projectId?: string,