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>

diffuser.html

@@ -16,9 +16,9 @@ RED.nodes.registerType('diffuser', {
     logLevel: { value: 'error' },
   },
   inputs: 1,
-  outputs: 4,
+  outputs: 3,
   inputLabels: ['control'],
-  outputLabels: ['process', 'dbase', 'reactor control', 'parent'],
+  outputLabels: ['process', 'dbase', 'parent'],
   icon: 'font-awesome/fa-tint',
   label: function() {
     return this.name ? `${this.name}_${this.number}` : 'diffuser';