feat(frontend): add task details edit flow

Add a task details action from the entity page and route it to a prefilled edit task page.

Extend the local task API with single-task read and update helpers, and cover the new flow with frontend tests.

frontend/src/pages/EntityDetailPage.tsx

@@ -67,6 +67,14 @@ export default function EntityDetailPage() {
               <p className="text-sm text-slate-400">
                 Email context: {getEmailLookbackLabel(task.emailLookback)}
               </p>
+              <div className="pt-2">
+                <Link
+                  to={`/entities/${entityId}/tasks/${task.id}`}
+                  className="inline-flex rounded-md border border-slate-700 px-3 py-1.5 text-sm text-slate-200 hover:border-cyan-500 hover:text-cyan-300"
+                >
+                  Details
+                </Link>
+              </div>
             </li>
           ))}
           {tasks.length === 0 && (