docs(phpdoc): document public methods across src/

Add professional PHPDoc (summary + @param/@return) to the remaining
public methods that had none or only partial coverage: GraphController's
actions, ContributionStore's accessors, SvgRenderer's render() and
private helpers (with concrete array-shape annotations), ProbeTrait,
ProviderHealthChecker, ProviderStatus, and the Contribution entity.
Also adds the matching @return shapes on SvgRendererTest's data
providers.

src/Controller/GraphController.php

@@ -34,8 +34,12 @@ final class GraphController
     }
 
     /**
-     * Query parameters:
-     *   theme  string  dark|light (default: dark)
+     * Serves the contribution heatmap SVG, from a 1-hour cache on repeat requests.
+     *
+     * Rejects requests to disallowed hosts (ALLOWED_HOSTS env) with a 403.
+     *
+     * @param  Request $request query parameter `theme` selects "dark" (default) or "light"
+     * @return Response image/svg+xml body, cacheable for 3600s
      */
     #[Route('/graph.svg', name: 'contribution_graph', methods: ['GET'])]
     public function graph(Request $request): Response
@@ -66,6 +70,12 @@ final class GraphController
         ]);
     }
 
+    /**
+     * Redirects "/" to "/graph.svg", forwarding any query string (e.g. ?theme=light).
+     *
+     * @param  Request          $request incoming request whose query string is preserved
+     * @return RedirectResponse 302 redirect to /graph.svg
+     */
     #[Route('/', name: 'index', methods: ['GET'])]
     public function index(Request $request): RedirectResponse
     {
@@ -75,6 +85,12 @@ final class GraphController
         return new RedirectResponse($url, 302);
     }
 
+    /**
+     * Reports per-provider connectivity status as JSON.
+     *
+     * @return Response 200 with {"status":"ok",...} or 503 with {"status":"degraded",...}
+     *                  when any configured provider's probe reports an error
+     */
     #[Route('/health', name: 'health', methods: ['GET'])]
     public function health(): Response
     {