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>

test/basic/groupCurves.basic.test.js

@@ -0,0 +1,66 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const { groupFlow, groupPower, groupNCog, groupCalcPower } = require('../../src/groupOps/groupCurves');
+
+function predictView(min, max, current = (min + max) / 2) {
+    return {
+        currentF: current,
+        currentFxyYMin: min,
+        currentFxyYMax: max,
+    };
+}
+
+test('groupFlow returns the same shape as the original _groupFlow (groupPredictFlow preferred)', () => {
+    const machine = {
+        predictFlow:      predictView(0, 1, 0.5),
+        groupPredictFlow: predictView(0.1, 0.9, 0.4),
+    };
+    const v = groupFlow(machine);
+    assert.equal(v, machine.groupPredictFlow);
+    assert.equal(v.currentFxyYMin, 0.1);
+    assert.equal(v.currentFxyYMax, 0.9);
+    assert.equal(v.currentF, 0.4);
+});
+
+test('groupFlow falls back to predictFlow when groupPredictFlow is absent', () => {
+    const machine = { predictFlow: predictView(0, 1) };
+    assert.equal(groupFlow(machine), machine.predictFlow);
+});
+
+test('groupPower returns groupPredictPower when present, else predictPower', () => {
+    const m1 = { predictPower: predictView(0, 100), groupPredictPower: predictView(10, 90) };
+    assert.equal(groupPower(m1), m1.groupPredictPower);
+
+    const m2 = { predictPower: predictView(0, 100) };
+    assert.equal(groupPower(m2), m2.predictPower);
+});
+
+test('groupNCog returns the group value when groupPredictFlow is present', () => {
+    const m = { groupPredictFlow: predictView(0, 1), groupNCog: 0.42, NCog: 0.99, predictFlow: predictView(0, 1) };
+    assert.equal(groupNCog(m), 0.42);
+});
+
+test('groupNCog falls back to NCog when no groupPredictFlow', () => {
+    const m = { predictFlow: predictView(0, 1), NCog: 0.7 };
+    assert.equal(groupNCog(m), 0.7);
+});
+
+test('groupNCog defaults to 0 when neither is defined', () => {
+    const m = { predictFlow: predictView(0, 1) };
+    assert.equal(groupNCog(m), 0);
+});
+
+test('groupCalcPower prefers machine.groupCalcPower', () => {
+    let lastFlow = null;
+    const m = {
+        groupCalcPower(flow) { lastFlow = flow; return flow * 2; },
+        inputFlowCalcPower(flow) { return flow * 999; },
+    };
+    assert.equal(groupCalcPower(m, 0.3), 0.6);
+    assert.equal(lastFlow, 0.3);
+});
+
+test('groupCalcPower falls back to inputFlowCalcPower when groupCalcPower missing', () => {
+    const m = { inputFlowCalcPower(flow) { return flow + 1; } };
+    assert.equal(groupCalcPower(m, 5), 6);
+});