feat: level-based control now reaches machine groups + manual Qd forwarding

Two additions to pumpingStation:

1. _controlLevelBased now calls _applyMachineGroupLevelControl in
   addition to _applyMachineLevelControl when the basin is filling
   above startLevel. Previously only direct-child machines received
   the level-based percent-control signal; in a hierarchical topology
   (PS → MGC → pumps) the machines sit under MGC and PS.machines is
   empty, so the level control never reached them.

2. New 'Qd' input topic + forwardDemandToChildren() method. When PS
   is in 'manual' mode (matching the pattern from rotatingMachine's
   virtualControl), operator demand from a dashboard slider is forwarded
   to all child machine groups and direct machines. When PS is in any
   other mode (levelbased, flowbased, etc.), the Qd msg is silently
   dropped with a debug log so the automatic control isn't overridden.

No breaking changes — existing flows that don't send 'Qd' are unaffected,
and _controlLevelBased's additional call to machineGroupLevelControl
is a no-op when no machine groups are registered.

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

src/nodeClass.js

@@ -221,6 +221,27 @@ class nodeClass {
           this.source.setManualInflow(val, ts, unit);
           break;
         }
+        case 'Qd': {
+          // Manual demand: operator sets the target output via a
+          // dashboard slider. Only accepted when PS is in 'manual'
+          // mode — mirrors how rotatingMachine gates commands by
+          // mode (virtualControl vs auto).
+          const demand = Number(msg.payload);
+          if (!Number.isFinite(demand)) {
+            this.source.logger.warn(`Invalid Qd value: ${msg.payload}`);
+            break;
+          }
+          if (this.source.mode === 'manual') {
+            this.source.forwardDemandToChildren(demand).catch((err) =>
+              this.source.logger.error(`Failed to forward demand: ${err.message}`)
+            );
+          } else {
+            this.source.logger.debug(
+              `Qd ignored in ${this.source.mode} mode. Switch to manual to use the demand slider.`
+            );
+          }
+          break;
+        }
       }
       done();
     });