fix(plating): add 3 missing icons to process.node Selection

fp.step.template rows already held 'fa-bathtub' (1), 'fa-flag' (2),
and 'fa-undo' (2) — all plating-relevant and presumably valid in an
earlier version of the Selection list. When step_insert snapshot-
copied these into a fresh fusion.plating.process.node via
_copy_snapshot_fields, the ORM rejected them with
ValueError: Wrong value for fusion.plating.process.node.icon
because they weren't in the curated 39-icon list anymore.

Adding 'fa-bathtub' (bathtub / tank / soak), 'fa-flag' (flag /
milestone / gate), and 'fa-undo' (undo / rework / rerun) to the
process.node Selection. Aligns the two lists (template uses
_get_icon_selection -> node._fields['icon'].selection at runtime).

No data migration needed — existing template rows immediately
re-validate against the wider Selection.

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

fusion_plating/fusion_plating/__manifest__.py

@@ -5,7 +5,7 @@
 
 {
     'name': 'Fusion Plating',
-    'version': '19.0.22.0.0',
+    'version': '19.0.22.1.0',
     'category': 'Manufacturing/Plating',
     'summary': 'Core plating / metal finishing ERP: facilities, processes, tanks, baths, jobs, operators.',
     'description': """