feat(KB-041): add task refine capability across core, API, UI, and CLI

- Add refineTask() to TaskStore with validation for feedback and requirements
- Add POST /tasks/:id/refine API endpoint with tests
- Add refine UI to TaskDetailModal for submitting feedback
- Add kb_task_refine tool to pi extension for AI-driven refinement
- Add 'kb task refine' CLI command for manual task refinement
- Include validation constraints: max 2000 chars feedback, max 5000 chars requirements

packages/dashboard/app/api.ts

@@ -140,6 +140,13 @@ export function requestSpecRevision(id: string, feedback: string): Promise<Task>
   });
 }
 
+export function refineTask(id: string, feedback: string): Promise<Task> {
+  return api<Task>(`/tasks/${id}/refine`, {
+    method: "POST",
+    body: JSON.stringify({ feedback }),
+  });
+}
+
 // --- Models API ---
 
 /** Available AI model info returned by the models endpoint */