P4 wave 1: extract MGC concerns into focused modules

src/groupOps/        groupOperatingPoint + groupCurves (pure functions)
  src/totals/          totalsCalculator (dynamic + absolute + active)
  src/combinatorics/   pumpCombinations (validPumpCombinations + checkSpecialCases)
  src/optimizer/       bestCombination (CoG) + bepGravitation (BEP-G + marginal-cost)
  src/efficiency/      groupEfficiency (calc + distance helpers)
  src/dispatch/        demandDispatcher (LatestWinsGate-based; replaces
                       _dispatchInFlight + _delayedCall)
  src/commands/        canonical names from start (set.mode/scaling/demand,
                       child.register) + legacy aliases
  CONTRACT.md          inputs/outputs/events surface

53 basic tests pass (52 new + 1 pre-existing).
specificClass.js / nodeClass.js untouched — integration in P4 wave 2.

Findings flagged via agents (TODO append to OPEN_QUESTIONS.md):
  - calcGroupEfficiency.maxEfficiency is actually the mean (misleading name)
  - checkSpecialCases has a no-op `return false` inside forEach
  - MGC doesn't route cmd.startup/shutdown/estop — confirm if station broadcasts need it

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/commands/index.js

@@ -0,0 +1,37 @@
+'use strict';
+
+// machineGroupControl command registry. Consumed by BaseNodeAdapter via
+// `static commands = require('./commands')`. Each descriptor maps a
+// canonical msg.topic to its handler; legacy names are listed under
+// `aliases` and emit a one-time deprecation warning at runtime.
+
+const handlers = require('./handlers');
+
+module.exports = [
+  {
+    topic: 'set.mode',
+    aliases: ['setMode'],
+    payloadSchema: { type: 'string' },
+    handler: handlers.setMode,
+  },
+  {
+    topic: 'set.scaling',
+    aliases: ['setScaling'],
+    payloadSchema: { type: 'string' },
+    handler: handlers.setScaling,
+  },
+  {
+    topic: 'child.register',
+    aliases: ['registerChild'],
+    // payload is the Node-RED id (string) of the child node.
+    payloadSchema: { type: 'string' },
+    handler: handlers.registerChild,
+  },
+  {
+    topic: 'set.demand',
+    aliases: ['Qd'],
+    // any: number or numeric string — handler runs parseFloat.
+    payloadSchema: { type: 'any' },
+    handler: handlers.setDemand,
+  },
+];