Add Redis cache for Meilisearch search results and admin dashboard stats

- Configure Redis DB 2 as Symfony cache adapter
- Cache Meilisearch search results for 5 minutes (invalidated on writes)
- Cache admin dashboard stats for 10 minutes
- Add invalidateSearchCache() called after each Meilisearch write
- Update tests to support cache mock injection

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.env.test

@@ -13,5 +13,6 @@ STRIPE_WEBHOOK_SECRET_CONNECT=whsec_test_connect
 OUTSIDE_URL=https://test.example.com
 MESSENGER_TRANSPORT_DSN=redis://:e_ticket@redis:6379/messages
 SESSION_HANDLER_DSN=redis://:e_ticket@redis:6379/1
+REDIS_CACHE_DSN=redis://:e_ticket@redis:6379/2
 SMIME_PASSPHRASE=test
 ADMIN_EMAIL=contact@test.com