feat(rust): doctor says what a missing ZoneDomes helper costs

RunicGatewayDomes.cs (PLAN_REDESIGNS §3.2, D194) ships beside the bridge
from the next plugin release; the installer already places every helper
the manifest lists. doctor now names its absence in the operator's words:
zones still open, but the site offers no dome.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

src/rustgame/doctor.rs

@@ -314,6 +314,11 @@ fn helper_absence(name: &str) -> String {
              own flags miss anybody already standing in a zone when it is created or restored"
                 .to_string()
         }
+        "RunicGatewayDomes.cs" => {
+            "the bridge still runs and its zones still open, but the site offers no dome over \
+             an event zone, because ZoneDomes cannot be called without it"
+                .to_string()
+        }
         _ => format!("the bridge still runs without {name}; what it helped with falls back"),
     }
 }