fix: replace Janitor wording with reclaim/prune actions in user-facing copy (#1518)

Rename "Janitor threshold" to "Reclaimable Docker data threshold" in Settings
and update the unused-Docker-data alert to point users to the Resources view
and the Prune Node Resources scheduled action, which are the real UI surfaces
for reclaiming disk space. Remove "janitor" from settings search keywords.
The internal docker_janitor_gb database key and JANITOR_* constants are
unchanged.

backend/src/services/MonitorService.ts

@@ -450,7 +450,7 @@ export class MonitorService {
                     JANITOR_COOLDOWN_MS,
                     'info',
                     'system',
-                    `Node "${nodeLabel}" has accumulated ${reclaimGb.toFixed(1)} GB of unused Docker data. Consider using the Janitor tool.`,
+                    `Node "${nodeLabel}" has accumulated ${reclaimGb.toFixed(1)} GB of unused Docker data. Open Resources to reclaim space, or set up a Prune Node Resources schedule.`,
                 );
             }
         } finally {