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

app/Http/Controllers/Api/ArtworkInteractionController.php

@@ -120,6 +120,27 @@ final class ArtworkInteractionController extends Controller
         ]);
     }
 
+    /**
+     * POST /api/artworks/{id}/share — record a share event (Phase 2 tracking).
+     */
+    public function share(Request $request, int $artworkId): JsonResponse
+    {
+        $data = $request->validate([
+            'platform' => ['required', 'string', 'in:facebook,twitter,pinterest,email,copy,embed'],
+        ]);
+
+        if (Schema::hasTable('artwork_shares')) {
+            DB::table('artwork_shares')->insert([
+                'artwork_id' => $artworkId,
+                'user_id'    => $request->user()?->id,
+                'platform'   => $data['platform'],
+                'created_at' => now(),
+            ]);
+        }
+
+        return response()->json(['ok' => true]);
+    }
+
     private function toggleSimple(
         Request $request,
         string $table,