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_quality/models/__init__.py

@@ -9,6 +9,7 @@ from . import fp_calibration
 from . import fp_calibration_event
 from . import fp_avl
 from . import fp_customer_spec
+from . import fp_process_node_inherit
 from . import fp_audit
 from . import fp_fair
 from . import fp_doc_control