fix(web): make managed process reaper async

packages/web/server/lib/opencode/lifecycle.test.js

@@ -6,6 +6,11 @@ const spawnMock = vi.fn();
 vi.mock('node:child_process', () => ({
   spawn: spawnMock,
   spawnSync: vi.fn(),
+  // `managed-process-registry.js` (imported transitively via lifecycle.js)
+  // calls `promisify(execFile)` at module load, so the mock must expose a
+  // function here. Lifecycle tests don't exercise the reaper path, so a plain
+  // stub is enough; the registry's best-effort writes are no-ops on errors.
+  execFile: vi.fn(),
 }));
 
 const { createOpenCodeLifecycleRuntime } = await import('./lifecycle.js');