refactor: reorganise Service/ into Provider/ and Renderer/ sub-namespaces

Move all provider-related classes, enums, interface and trait into
App\Service\Provider; move SvgRenderer into App\Service\Renderer.
ContributionAggregator stays at the Service root as the orchestrator.
Test namespaces and use statements updated to match.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Service/ContributionAggregator.php

@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace App\Service;
 
+use App\Service\Provider\ProviderInterface;
 use Psr\Log\LoggerInterface;
 use Symfony\Component\DependencyInjection\Attribute\AutowireIterator;