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

routes/api.php

@@ -258,6 +258,13 @@ Route::middleware(['web', 'auth', 'normalize.username'])->group(function () {
         ->name('api.users.follow');
 });
 
+// ── Share tracking (public, throttled) ────────────────────────────────────────
+// POST /api/artworks/{id}/share   → record a share event
+Route::middleware(['web', 'throttle:30,1'])
+    ->post('artworks/{id}/share', [\App\Http\Controllers\Api\ArtworkInteractionController::class, 'share'])
+    ->whereNumber('id')
+    ->name('api.artworks.share');
+
 // ── Comment CRUD ──────────────────────────────────────────────────────────────
 // GET    /api/artworks/{id}/comments                  list comments (public)
 // POST   /api/artworks/{id}/comments                  post a comment (auth)