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/components/ui/ShareToast.jsx

@@ -0,0 +1,55 @@
+import React, { useEffect, useState } from 'react'
+import { createPortal } from 'react-dom'
+
+/**
+ * ShareToast — a minimal, auto-dismissing toast notification.
+ *
+ * Props:
+ *   message   – text to display
+ *   visible   – whether the toast is currently shown
+ *   onHide    – callback when the toast finishes (auto-hidden after ~2 s)
+ *   duration  – ms before auto-dismiss (default 2000)
+ */
+export default function ShareToast({ message = 'Link copied!', visible = false, onHide, duration = 2000 }) {
+  const [show, setShow] = useState(false)
+
+  useEffect(() => {
+    if (visible) {
+      // Small delay so the enter transition plays
+      const enterTimer = requestAnimationFrame(() => setShow(true))
+      const hideTimer = setTimeout(() => {
+        setShow(false)
+        setTimeout(() => onHide?.(), 200) // let exit transition finish
+      }, duration)
+
+      return () => {
+        cancelAnimationFrame(enterTimer)
+        clearTimeout(hideTimer)
+      }
+    } else {
+      setShow(false)
+    }
+  }, [visible, duration, onHide])
+
+  if (!visible) return null
+
+  return createPortal(
+    <div
+      role="status"
+      aria-live="polite"
+      className={[
+        'fixed bottom-24 left-1/2 z-[10001] -translate-x-1/2 rounded-full border border-white/[0.10] bg-nova-800/90 px-5 py-2.5 text-sm font-medium text-white shadow-xl backdrop-blur-md transition-all duration-200',
+        show ? 'translate-y-0 opacity-100' : 'translate-y-3 opacity-0',
+      ].join(' ')}
+    >
+      <span className="flex items-center gap-2">
+        {/* Check icon */}
+        <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 20" fill="currentColor" className="h-4 w-4 text-emerald-400">
+          <path fillRule="evenodd" d="M16.704 4.153a.75.75 0 0 1 .143 1.052l-8 10.5a.75.75 0 0 1-1.127.075l-4.5-4.5a.75.75 0 0 1 1.06-1.06l3.894 3.893 7.48-9.817a.75.75 0 0 1 1.05-.143Z" clipRule="evenodd" />
+        </svg>
+        {message}
+      </span>
+    </div>,
+    document.body,
+  )
+}