feat: artwork share system with modal, native Web Share API, and tracking

- Add ArtworkShareModal with glassmorphism UI (Facebook, X, Pinterest, Email, Copy Link, Embed Code)
- Add ArtworkShareButton with lazy-loaded modal and native share fallback
- Add useWebShare hook abstracting navigator.share with AbortError handling
- Add ShareToast auto-dismissing notification component
- Add share() endpoint to ArtworkInteractionController (POST /api/artworks/{id}/share)
- Add artwork_shares migration for Phase 2 share tracking
- Refactor ArtworkActionBar to use new ArtworkShareButton component

resources/js/hooks/useWebShare.js

@@ -0,0 +1,41 @@
+import { useCallback, useMemo } from 'react'
+
+/**
+ * useWebShare – abstracts native Web Share API with a fallback callback.
+ *
+ * Usage:
+ *   const { canNativeShare, share } = useWebShare({ onFallback })
+ *   share({ title, text, url })
+ *
+ * If `navigator.share` is available the browser-native share sheet opens.
+ * Otherwise `onFallback({ title, text, url })` is called (e.g. open a modal).
+ */
+export default function useWebShare({ onFallback } = {}) {
+  const canNativeShare = useMemo(
+    () => typeof navigator !== 'undefined' && typeof navigator.share === 'function',
+    [],
+  )
+
+  const share = useCallback(
+    async ({ title, text, url }) => {
+      if (canNativeShare) {
+        try {
+          await navigator.share({ title, text, url })
+          return { shared: true, native: true }
+        } catch (err) {
+          // User cancelled the native share — don't fall through to modal
+          if (err?.name === 'AbortError') {
+            return { shared: false, native: true }
+          }
+        }
+      }
+
+      // Fallback — open modal
+      onFallback?.({ title, text, url })
+      return { shared: false, native: false }
+    },
+    [canNativeShare, onFallback],
+  )
+
+  return { canNativeShare, share }
+}