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/useShare/index.ts

@@ -0,0 +1,102 @@
+import { toValue } from 'vue';
+import type { MaybeRefOrGetter, Ref } from 'vue';
+import { defaultNavigator } from '@/types';
+import type { ConfigurableNavigator } from '@/types';
+import { useSupported } from '@/composables/browser/useSupported';
+
+export interface UseShareOptions {
+  /**
+   * Title of the shared content
+   */
+  title?: string;
+
+  /**
+   * Arbitrary text that forms the body of the message being shared
+   */
+  text?: string;
+
+  /**
+   * URL string referring to a resource being shared
+   */
+  url?: string;
+
+  /**
+   * Array of `File` objects representing files to be shared
+   */
+  files?: File[];
+}
+
+/**
+ * Subset of `Navigator` exposing the Web Share API surface, which is not yet in
+ * every lib DOM target.
+ */
+interface NavigatorWithShare {
+  share?: (data?: UseShareOptions) => Promise<void>;
+  canShare?: (data?: UseShareOptions) => boolean;
+}
+
+export interface UseShareReturn {
+  /**
+   * Whether the Web Share API is available
+   */
+  isSupported: Readonly<Ref<boolean>>;
+
+  /**
+   * Invoke the native share sheet, optionally merging `overrideData` over the
+   * default share options. Resolves once sharing finishes (or is skipped when
+   * unsupported / the payload cannot be shared).
+   */
+  share: (overrideData?: MaybeRefOrGetter<UseShareOptions>) => Promise<void>;
+}
+
+/**
+ * @name useShare
+ * @category Browser
+ * @description Reactive Web Share API wrapper to invoke the native share sheet.
+ *
+ * @param {MaybeRefOrGetter<UseShareOptions>} [shareOptions={}] Default share payload (title, text, url, files)
+ * @param {UseShareOptions} [options={}] Options
+ * @returns {UseShareReturn} `isSupported` flag and a `share` method
+ *
+ * @example
+ * const { share, isSupported } = useShare({ title: 'Hello', url: location.href });
+ * share();
+ *
+ * @example
+ * // Override the default payload per call
+ * const { share } = useShare({ title: 'Default' });
+ * share({ text: 'One-off message' });
+ *
+ * @since 0.0.15
+ */
+export function useShare(
+  shareOptions: MaybeRefOrGetter<UseShareOptions> = {},
+  options: ConfigurableNavigator = {},
+): UseShareReturn {
+  const { navigator = defaultNavigator } = options;
+
+  const _navigator = navigator as NavigatorWithShare | undefined;
+  const isSupported = useSupported(() => !!_navigator && 'canShare' in _navigator);
+
+  const share = async (overrideData: MaybeRefOrGetter<UseShareOptions> = {}): Promise<void> => {
+    if (!isSupported.value || !_navigator)
+      return;
+
+    const data: UseShareOptions = {
+      ...toValue(shareOptions),
+      ...toValue(overrideData),
+    };
+
+    // `canShare` gates the payload (e.g. file types / size); only proceed when it
+    // accepts the data to avoid a guaranteed-to-reject `share()` call.
+    if (_navigator.canShare && !_navigator.canShare(data))
+      return;
+
+    return _navigator.share?.(data);
+  };
+
+  return {
+    isSupported,
+    share,
+  };
+}