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/Provider/ProviderInterface.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Service\Provider;
+
+interface ProviderInterface
+{
+    /** @return array<string, int>  date (Y-m-d) => contribution count */
+    public function fetch(): array;
+
+    public function isConfigured(): bool;
+
+    public function getName(): string;
+
+    public function probe(): ProviderStatus;
+
+    public function ping(): void;
+}