feat(KB-040): add break-into-subtasks toggle for task creation

- Add breakIntoSubtasks flag to core Task model and persist to store
- Plumb subtask flag through dashboard API routes with validation
- Add subtask toggle UI to inline task creation card
- Update triage agent to handle automatic subtask breakdown when enabled
- Add comprehensive tests for store, API routes, and UI components
- Include changeset for patch release documenting the new feature

packages/dashboard/app/api.ts

@@ -32,9 +32,16 @@ export async function fetchTaskDetail(id: string): Promise<TaskDetail> {
 }
 
 export function createTask(input: TaskCreateInput): Promise<Task> {
+  const { title, description, column, dependencies, breakIntoSubtasks } = input;
   return api<Task>("/tasks", {
     method: "POST",
-    body: JSON.stringify(input),
+    body: JSON.stringify({
+      title,
+      description,
+      column,
+      dependencies,
+      breakIntoSubtasks,
+    }),
   });
 }