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/artwork/ArtworkActionBar.jsx

@@ -1,5 +1,6 @@
 import React, { useEffect, useRef, useState } from 'react'
 import { createPortal } from 'react-dom'
+import ArtworkShareButton from './ArtworkShareButton'
 
 function formatCount(value) {
   const n = Number(value || 0)
@@ -49,13 +50,7 @@ function DownloadArrowIcon() {
   )
 }
 
-function ShareIcon() {
-  return (
-    <svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" strokeWidth={1.5} stroke="currentColor" className="h-5 w-5">
-      <path strokeLinecap="round" strokeLinejoin="round" d="M8.684 13.342C8.886 12.938 9 12.482 9 12c0-.482-.114-.938-.316-1.342m0 2.684a3 3 0 1 1 0-2.684m0 2.684 6.632 3.316m-6.632-6 6.632-3.316m0 0a3 3 0 1 0 5.367-2.684 3 3 0 0 0-5.367 2.684Zm0 9.316a3 3 0 1 0 5.368 2.684 3 3 0 0 0-5.368-2.684Z" />
-    </svg>
-  )
-}
+/* ShareIcon removed — now provided by ArtworkShareButton */
 
 function FlagIcon() {
   return (
@@ -201,8 +196,6 @@ export default function ArtworkActionBar({ artwork, stats, canonicalUrl, onStats
   const [reporting, setReporting] = useState(false)
   const [reported, setReported] = useState(false)
   const [reportOpen, setReportOpen] = useState(false)
-  const [copied, setCopied] = useState(false)
-
   useEffect(() => {
     setFavorited(Boolean(artwork?.viewer?.is_favorited))
   }, [artwork?.id, artwork?.viewer?.is_favorited])
@@ -272,18 +265,6 @@ export default function ArtworkActionBar({ artwork, stats, canonicalUrl, onStats
     } catch { setFavorited(!nextState) }
   }
 
-  const onShare = async () => {
-    try {
-      if (navigator.share) {
-        await navigator.share({ title: artwork?.title || 'Artwork', url: shareUrl })
-        return
-      }
-      await navigator.clipboard.writeText(shareUrl)
-      setCopied(true)
-      setTimeout(() => setCopied(false), 2000)
-    } catch { /* noop */ }
-  }
-
   const openReport = () => {
     if (reported) return
     setReportOpen(true)
@@ -330,15 +311,7 @@ export default function ArtworkActionBar({ artwork, stats, canonicalUrl, onStats
         </div>
 
         {/* Share pill */}
-        <button
-          type="button"
-          aria-label="Share artwork"
-          onClick={onShare}
-          className="inline-flex items-center gap-2 rounded-full border border-white/[0.08] bg-white/[0.04] px-5 py-2.5 text-sm font-medium text-white/70 transition-all duration-200 hover:border-white/[0.15] hover:bg-white/[0.07] hover:text-white"
-        >
-          <ShareIcon />
-          {copied ? 'Copied!' : 'Share'}
-        </button>
+        <ArtworkShareButton artwork={artwork} shareUrl={shareUrl} size="default" />
 
         {/* Report pill */}
         <button
@@ -389,14 +362,7 @@ export default function ArtworkActionBar({ artwork, stats, canonicalUrl, onStats
           </button>
 
           {/* Share */}
-          <button
-            type="button"
-            aria-label="Share"
-            onClick={onShare}
-            className="inline-flex items-center gap-1.5 rounded-full border border-white/[0.08] bg-white/[0.04] px-3.5 py-2 text-xs font-medium text-white/70 transition-all"
-          >
-            <ShareIcon />
-          </button>
+          <ArtworkShareButton artwork={artwork} shareUrl={shareUrl} size="small" />
 
           {/* Report */}
           <button