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/models/fp_process_node.py

@@ -336,6 +336,68 @@ class FpProcessNode(models.Model):
     # NB. `pricing_rule_ids` lives in fusion_plating_configurator
     # (added there so this core module doesn't depend on the configurator).
 
+    # ---- Spec-derived metadata (recipe-root only — Promote Customer Spec) ----
+    # These were on fp.coating.config (since retired). They describe the
+    # PROCESS the recipe runs, not the customer-facing specification —
+    # specs live on fusion.plating.customer.spec.
+    phosphorus_level = fields.Selection(
+        [('low_phos', 'Low Phosphorus (2-5%)'),
+         ('mid_phos', 'Mid Phosphorus (6-9%)'),
+         ('high_phos', 'High Phosphorus (10-13%)'),
+         ('na', 'N/A')],
+        string='Phosphorus Level',
+        default='na',
+        help='EN-specific. Set to N/A for non-EN processes (chrome, '
+             'anodize, black oxide). Drives certificate annotation and '
+             'hydrogen-embrittlement risk assessment for bake-relief.',
+    )
+    thickness_min = fields.Float(string='Min Thickness', digits=(10, 4))
+    thickness_max = fields.Float(string='Max Thickness', digits=(10, 4))
+    thickness_uom = fields.Selection(
+        [('mils', 'mils'), ('microns', 'microns'), ('inches', 'inches')],
+        string='Thickness UoM', default='mils',
+    )
+    thickness_option_ids = fields.One2many(
+        'fp.recipe.thickness',
+        'recipe_id',
+        string='Thickness Options',
+        help='Discrete thickness values offered to the estimator on the '
+             'order line for jobs running this recipe.',
+    )
+
+    # ---- Bake relief — AMS 2759/9 hydrogen embrittlement (recipe root) ----
+    requires_bake_relief = fields.Boolean(
+        string='Requires Bake Relief',
+        help='Hydrogen embrittlement relief bake required (high-strength '
+             'steel ≥ HRC 31 in conjunction with this chemistry). When '
+             'set, finishing the job auto-creates a bake-window record '
+             'and blocks shipment until bake is complete.',
+    )
+    bake_window_hours = fields.Float(
+        string='Bake Window (hours)', default=4.0,
+        help='Maximum time between plate exit and bake start. Typical 4h '
+             'per AMS 2759/9.',
+    )
+    bake_temperature = fields.Float(
+        string='Bake Temperature', default=375.0,
+        help='Relief bake temperature. Default 375 (°F per AMS 2759/9 for '
+             'steel ≥ HRC 40).',
+    )
+    bake_temperature_uom = fields.Selection(
+        [('F', '°F'), ('C', '°C')],
+        string='Bake Temp Unit',
+        default='F',
+    )
+    bake_duration_hours = fields.Float(
+        string='Bake Duration (hours)', default=23.0,
+        help='Minimum bake hold time at temperature. Typical 23h.',
+    )
+
+    # NB. `applicable_spec_ids` (reverse of customer.spec.recipe_ids) is
+    # defined as an inherit in fusion_plating_quality (the module that
+    # owns fusion.plating.customer.spec). Core can't reference it
+    # directly without a dependency inversion.
+
     # ---- Computed fields -----------------------------------------------------
 
     display_name = fields.Char(