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

database/migrations/2026_02_28_000002_create_artwork_shares_table.php

@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('artwork_shares', function (Blueprint $table) {
+            $table->id();
+            $table->unsignedBigInteger('artwork_id');
+            $table->unsignedBigInteger('user_id')->nullable();
+            $table->string('platform', 32); // facebook, twitter, pinterest, copy, email, embed
+            $table->timestamp('created_at')->useCurrent();
+
+            $table->index('artwork_id');
+            $table->index('platform');
+            $table->index(['artwork_id', 'platform']);
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('artwork_shares');
+    }
+};