Allow artworks to have one primary category and extra secondaries.

Keep artwork_category as membership, store a deterministic primary_category_id, and let upload plus studio pick up to five additional same-type categories without changing canonical URLs.

tests/Feature/ArtworkSearchDocumentTest.php

@@ -13,7 +13,6 @@ function createSearchDocumentContentType(string $name, int $sortOrder = 0): int
         'description' => null,
         'created_at' => now(),
         'updated_at' => now(),
-        'sort_order' => $sortOrder,
     ]);
 }
 
@@ -48,14 +47,17 @@ it('indexes all attached categories and content types while preserving a primary
     $mattePaintingId = createSearchDocumentCategory($digitalArtId, 'Matte Painting', 20);
 
     $artwork->categories()->sync([$mattePaintingId, $fantasyId]);
+    $artwork->forceFill(['primary_category_id' => $fantasyId])->save();
 
-    $payload = $artwork->fresh(['categories.contentType'])->toSearchableArray();
+    $payload = $artwork->fresh(['categories.contentType', 'primaryCategory.contentType'])->toSearchableArray();
     $fantasySlug = (string) DB::table('categories')->where('id', $fantasyId)->value('slug');
     $mattePaintingSlug = (string) DB::table('categories')->where('id', $mattePaintingId)->value('slug');
     $wallpapersSlug = (string) DB::table('content_types')->where('id', $wallpapersId)->value('slug');
     $digitalArtSlug = (string) DB::table('content_types')->where('id', $digitalArtId)->value('slug');
 
     expect($payload['category'])->toBe($fantasySlug)
+        ->and($payload['primary_category_id'])->toBe($fantasyId)
+        ->and($payload['category_ids'])->toEqualCanonicalizing([$fantasyId, $mattePaintingId])
         ->and($payload['content_type'])->toBe($wallpapersSlug)
         ->and($payload['categories'])->toBe([$fantasySlug, $mattePaintingSlug])
         ->and($payload['content_types'])->toBe([$wallpapersSlug, $digitalArtSlug]);