P6: convert settler to platform infrastructure

Refactor of settler to use BaseNodeAdapter + commandRegistry + statusBadge.
settler 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 +1,32 @@
+'use strict';
+
+// Handler functions for settler commands. Each handler receives:
+//   source: the Settler domain instance.
+//   msg:    the Node-RED input message.
+//   ctx:    { node, RED, send, logger } — provided by BaseNodeAdapter.
+//
+// Settler currently accepts no behavioural commands — the legacy
+// `registerChild` topic is handled by the BaseNodeAdapter input dispatch
+// via the generalFunctions registry (`child.register` canonical) and the
+// node never had a public set/cmd surface beyond that. Future
+// influent-injection or operator-override topics will land here.
+
+function _logger(source, ctx) {
+  return ctx?.logger || source?.logger || null;
+}
+
+// Allows operators / upstream nodes to push an influent stream directly,
+// bypassing the reactor stateChange path. Payload mirrors the reactor's
+// `getEffluent` shape: { F, C } where C is the 13-species concentration
+// vector. Either field may be omitted to update only the other.
+exports.dataInfluent = (source, msg, ctx) => {
+  const log = _logger(source, ctx);
+  const p = msg?.payload;
+  if (!p || typeof p !== 'object' || Array.isArray(p)) {
+    log?.warn?.(`data.influent expects an object {F, C}; got ${typeof p}`);
+    return;
+  }
+  if (typeof p.F === 'number' && Number.isFinite(p.F)) source.F_in = p.F;
+  if (Array.isArray(p.C)) source.Cs_in = [...p.C];
+  source.notifyOutputChanged();
+};