feat(promote-customer-spec): Phase A — recipe + spec foundation

- Add fp.recipe.thickness model (replaces fp.coating.thickness, scoped to recipe root)
- Add spec metadata + bake-relief fields to fusion.plating.process.node (recipe root):
  phosphorus_level, thickness_min/max/uom, thickness_option_ids,
  requires_bake_relief + bake_window_hours/temperature/duration
- Add recipe_ids M2M + print_on_cert to fusion.plating.customer.spec
- Add applicable_spec_ids reverse M2M as inherit in fusion_plating_quality
  (avoids circular dep — core can't reference customer.spec which lives in quality)
- Surface new fields on recipe form ("Specification & Bake" notebook page)
- Surface recipe linkage on customer spec form

Pure additive. Foundation for Phases B-E.

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': '19.0.18.15.16',
+    'version': '19.0.19.0.0',
     'category': 'Manufacturing/Plating',
     'summary': 'Core plating / metal finishing ERP: facilities, processes, tanks, baths, jobs, operators.',
     'description': """
@@ -99,6 +99,7 @@ Copyright (c) 2026 Nexa Systems Inc. All rights reserved.
         'views/fp_facility_views.xml',
         'views/fp_bath_views.xml',
         'views/fp_process_node_views.xml',
+        'views/fp_recipe_thickness_views.xml',
         # Sub 14b — fp.step.kind catalog. MUST load before
         # fp_step_template_data.xml (templates reference kinds via
         # kind_id) AND before fp_step_template_views.xml (the form