test(dashboard): stub getSelfHealingManager on remote-access engine mock

server.ts createServer now invokes engine.getSelfHealingManager() to
wire the self-healing branch-rebind hook. The headless engine fake in
remote-access-headless.test.ts hadn't been updated. Add a vi.fn() stub
so the mock satisfies the engine surface contract.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/src/__tests__/remote-access-headless.test.ts

@@ -136,6 +136,7 @@ describe("remote access headless parity", () => {
       }),
       getMessageStore: vi.fn().mockReturnValue(undefined),
       getHeartbeatMonitor: vi.fn(),
+      getSelfHealingManager: vi.fn(),
       getWorkingDirectory: vi.fn().mockReturnValue("/fake/root"),
       getRoutineStore: vi.fn(),
       getRoutineRunner: vi.fn(),