healthz: depend on Publisher to force bundle deep-load (perfsmoke gap)

v0.1.0 shipped two bugs that left /healthz returning 200 against a
half-loaded bundle: the path-repo symlink dangling at runtime in the
AppImage (vendor/php-qml/bridge → nonexistent), and the writable
cache-dir bug (Symfony couldn't create var/cache/prod). HealthController
returned a static {status:"ok"} without ever touching any BridgeBundle
service, so perfsmoke + the connection-state probe both passed even
when the bundle's autoload was broken — first sign of trouble was a
500 from /api/todos under real load.

Inject Publisher (the bundle's Mercure-publish wrapper) via constructor
and reference its FQN in the response body. Two effects:

  - Symfony's container resolves Publisher when the controller is
    instantiated; if the bundle's autoload is broken, the controller
    can't even construct, /healthz returns 500.
  - The response now includes `bundle: "PhpQml\Bridge\Publisher"` —
    proves to perfsmoke + dev console that the canary is live, not a
    cached static response.

Connection-state probe semantics unchanged: still 200 = Online,
non-200 = Reconnecting/Offline. Probe interval is 5s — Publisher's
construction is constant-time, no perf concern.

No new public API: /healthz response gained a `bundle` field
(additive, JSON parsers ignore unknown keys); 200 vs 500 boundary is
preserved. No existing consumer broken.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

framework/php/src/Controller/HealthController.php

@@ -4,18 +4,33 @@ declare(strict_types=1);
 
 namespace PhpQml\Bridge\Controller;
 
+use PhpQml\Bridge\Publisher;
 use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\Routing\Attribute\Route;
 
 /**
  * Readiness probe used by the Qt host to detect when the backend is up.
  * See PLAN.md §3 (*Startup*, step 4).
+ *
+ * Publisher is injected purely as a deep-health canary: if the bridge
+ * bundle's autoload or container wiring is broken (e.g. a packaging build
+ * with a dangling vendor path-repo symlink), this controller can't even
+ * be constructed, so /healthz fails 500 instead of misleadingly returning
+ * 200 against a half-loaded bundle.
  */
 final class HealthController
 {
+    public function __construct(
+        private readonly Publisher $publisher,
+    ) {
+    }
+
     #[Route('/healthz', name: 'php_qml_bridge_healthz', methods: ['GET'])]
     public function __invoke(): JsonResponse
     {
-        return new JsonResponse(['status' => 'ok']);
+        return new JsonResponse([
+            'status' => 'ok',
+            'bundle' => $this->publisher::class,
+        ]);
     }
 }