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/fp_customer_spec.py

@@ -74,6 +74,22 @@ class FpCustomerSpec(models.Model):
     notes = fields.Html(
         string='Notes',
     )
+    recipe_ids = fields.Many2many(
+        'fusion.plating.process.node',
+        'fp_customer_spec_recipe_rel',
+        'spec_id', 'recipe_id',
+        domain="[('node_type', '=', 'recipe'), ('parent_id', '=', False)]",
+        string='Applicable Recipes',
+        help='Recipes that can produce work to this specification. '
+             'Many-to-many — one spec can cover multiple processes; '
+             'one recipe can satisfy multiple specs.',
+    )
+    print_on_cert = fields.Boolean(
+        string='Print on Certificate',
+        default=True,
+        help="When enabled, this spec's code+revision appear on the CoC "
+             'when the spec is selected on the SO line.',
+    )
     company_id = fields.Many2one(
         'res.company',
         string='Company',