fix(17): resolve post-merge wave 2 integration issues

- SettingsSheet: void the navigate('/login') promise (react-router v7 returns Promise) — eslint no-floating-promises
- InstructionSheet.test: wrap SettingsSheet render in MemoryRouter — 17-05 added useNavigate() which needs Router context

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/pwa/src/components/SettingsSheet.tsx

@@ -142,7 +142,7 @@ export function SettingsSheet({ isOpen, onClose }: SettingsSheetProps) {
       // API failure does not block navigation — server cookie was cleared or already expired
     }
     onClose();
-    navigate('/login');
+    void navigate('/login');
   };
 
   const handleToggle = async () => {