P6: convert diffuser to BaseDomain + BaseNodeAdapter + concern split

Refactor of diffuser to use the platform infrastructure (BaseDomain, BaseNodeAdapter,
ChildRouter, commandRegistry, statusBadge). Extracts concerns into
focused modules per .claude/refactor/MODULE_SPLIT.md generic template.
Tests stay green; CONTRACT.md generated; legacy aliases preserved.

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

src/commands/index.js

@@ -0,0 +1,47 @@
+'use strict';
+
+// Diffuser command registry. Consumed by BaseNodeAdapter via
+// `static commands = require('./commands')`. Each descriptor maps a
+// canonical msg.topic to its handler; legacy names live under `aliases`
+// and emit a one-time deprecation warning at runtime.
+
+const handlers = require('./handlers');
+
+module.exports = [
+  {
+    topic: 'data.flow',
+    aliases: ['air_flow'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setFlow,
+  },
+  {
+    topic: 'set.density',
+    aliases: ['density'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setDensity,
+  },
+  {
+    topic: 'set.water-height',
+    aliases: ['height_water'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setWaterHeight,
+  },
+  {
+    topic: 'set.header-pressure',
+    aliases: ['header_pressure'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setHeaderPressure,
+  },
+  {
+    topic: 'set.elements',
+    aliases: ['elements'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setElements,
+  },
+  {
+    topic: 'set.alfa-factor',
+    aliases: ['alfaFactor'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setAlfaFactor,
+  },
+];