P6: convert reactor to platform infrastructure

Refactor of reactor to use BaseNodeAdapter + commandRegistry + statusBadge.
reactor follows the platform refactor plan in .claude/refactor/MODULE_SPLIT.md.
Tests stay green; CONTRACT.md generated; legacy aliases preserved.

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

src/commands/handlers.js

@@ -0,0 +1,25 @@
+'use strict';
+
+// Reactor input handlers. Each receives (source, msg, ctx) where source is
+// the Reactor domain and ctx is { node, RED, send, logger }. The handlers
+// either forward to engine setters or drive a synchronous state update.
+
+exports.dataClock = (source, msg) => {
+  source.updateState(msg.timestamp ?? Date.now());
+};
+
+exports.dataFluent     = (source, msg) => { source.setInfluent    = msg; };
+exports.dataOTR        = (source, msg) => { source.setOTR         = msg; };
+exports.dataTemperature = (source, msg) => { source.setTemperature = msg; };
+exports.dataDispersion = (source, msg) => { source.setDispersion  = msg; };
+
+exports.childRegister = (source, msg, ctx) => {
+  const childId = msg.payload;
+  const RED = ctx?.RED;
+  const childObj = RED?.nodes?.getNode?.(childId);
+  if (!childObj || !childObj.source) {
+    source?.logger?.warn?.(`registerChild skipped: missing child/source for id=${childId}`);
+    return;
+  }
+  source.childRegistrationUtils.registerChild(childObj.source, msg.positionVsParent);
+};