⚡️(admin) optimize recording view by selecting room at the SQL level

Use select_related on the room foreign key to avoid N+1 queries. This makes
Django perform a join between tables instead of triggering additional queries
per row, reducing complexity from O(n²) patterns to O(n) and significantly
improving performance.

src/backend/core/admin.py

@@ -208,6 +208,7 @@ class RecordingAdmin(admin.ModelAdmin):
         "worker_id",
     )
     list_filter = ["created_at"]
+    list_select_related = ("room",)
     readonly_fields = ["id", "created_at", "updated_at"]
     actions = [resend_notification]