feat(KB-003): add task steering feature with UI and prompt injection

- Add SteeringComment type to core types for user steering input
- Add addSteeringComment method to TaskStore with persistence
- Add POST /api/tasks/:id/steer endpoint for adding steering comments
- Add frontend API client and SteeringTab UI component
- Inject steering comments into execution prompt for agent guidance
- Add comprehensive tests for store, API, UI, and executor components
- Include changeset for patch release

packages/dashboard/app/api.ts

@@ -106,6 +106,13 @@ export function fetchAgentLogs(taskId: string): Promise<AgentLogEntry[]> {
   return api<AgentLogEntry[]>(`/tasks/${taskId}/logs`);
 }
 
+export function addSteeringComment(id: string, text: string): Promise<Task> {
+  return api<Task>(`/tasks/${id}/steer`, {
+    method: "POST",
+    body: JSON.stringify({ text }),
+  });
+}
+
 // --- Models API ---
 
 /** Available AI model info returned by the models endpoint */