fix(vue): eslint/tsconfig migration + resolve type errors

@robonen/vue (toolkit): migrate to eslint flat config + composite tsconfig;
fix composable + test type errors (writable computed returns, null guards,
overload-compatible signatures, typed test helpers) — all type-level.

vue/toolkit/src/composables/browser/index.ts

@@ -1,7 +1,58 @@
+export * from './onKeyStroke';
+export * from './useActiveElement';
+export * from './useBodyScrollLock';
+export * from './useClickOutside';
+export * from './useClipboard';
+export * from './useCloseWatcher';
+export * from './useColorMode';
+export * from './useDevicePixelRatio';
+export * from './useDocumentReadyState';
+export * from './useDocumentVisibility';
+export * from './useDropZone';
+export * from './useElementBounding';
+export * from './useElementHover';
+export * from './useElementSize';
+export * from './useElementVisibility';
+export * from './useEscapeKey';
 export * from './useEventListener';
+export * from './useEyeDropper';
+export * from './useFavicon';
+export * from './useFileDialog';
+export * from './useFocus';
 export * from './useFocusGuard';
+export * from './useFocusWithin';
 export * from './useFps';
+export * from './useFullscreen';
+export * from './useGeolocation';
+export * from './useIdle';
+export * from './useIntersectionObserver';
 export * from './useIntervalFn';
+export * from './useKeyModifier';
+export * from './useMagicKeys';
+export * from './useMediaQuery';
+export * from './useMouse';
+export * from './useMousePressed';
+export * from './useMutationObserver';
+export * from './useNetwork';
+export * from './useObjectUrl';
+export * from './useOnline';
+export * from './usePageLeave';
+export * from './usePermission';
+export * from './usePointer';
+export * from './usePreferredColorScheme';
+export * from './usePreferredDark';
 export * from './useRafFn';
+export * from './useResizeObserver';
+export * from './useScreenOrientation';
+export * from './useScroll';
+export * from './useScrollLock';
+export * from './useShare';
 export * from './useSupported';
+export * from './useSwipe';
 export * from './useTabLeader';
+export * from './useTextSelection';
+export * from './useTitle';
+export * from './useVibrate';
+export * from './useWindowFocus';
+export * from './useWindowScroll';
+export * from './useWindowSize';