feat(FN-1191): hot-swap active executor sessions on model changes

- Show resolved default executor, validator, and planning models in the task Model tab
- Pass merged settings into the Model tab from TaskDetailModal so default badges reflect effective runtime resolution
- Hot-swap active single-session executor models when task overrides change, including fallback to project defaults when overrides are cleared
- Add dashboard and executor tests for default model display, hot-swap behavior, fallback logic, and failure logging
- Document hot-swap behavior and limitations in AGENTS.md and add a patch changeset for @gsxdsm/fusion

packages/dashboard/app/components/TaskDetailModal.tsx

@@ -929,7 +929,7 @@ export function TaskDetailModal({
             </div>
           ) : activeTab === "model" ? (
             <div className="detail-section">
-              <ModelSelectorTab task={task} addToast={addToast} onTaskUpdated={onTaskUpdated} />
+              <ModelSelectorTab task={task} addToast={addToast} onTaskUpdated={onTaskUpdated} settings={settings} />
             </div>
           ) : activeTab === "logs" ? (
             <div className={`detail-section${logSubview === "agent-log" ? " detail-section--agent-log" : ""}`}>