feat(thickness): single Char range field — drop fp.recipe.thickness picker

Per client direction: every order is a thickness RANGE (e.g.
"0.0005-0.0008 mils" or "5-10 mils"), never a single value. The
old picker model (fp.recipe.thickness with a single 'value' Float)
was modelling the wrong concept and overcrowding the order entry
UI. Replaced with one free-text Char field that auto-fills from
last-used or part default.

DELETED entirely:
- fp.recipe.thickness model (file + view + ACL + manifest entry)
- recipe.thickness_option_ids One2many (the picker source)
- "Thickness Options" inline list on the recipe form
- sale.order.line.x_fc_thickness_id (M2O picker)
- account.move.line.x_fc_thickness_id
- fp.delivery.x_fc_thickness_id
- fp.direct.order.line.thickness_id

ADDED:
- sale.order.line.x_fc_thickness_range (Char) — operator types range
- account.move.line.x_fc_thickness_range — for invoice rendering
- fp.delivery.x_fc_thickness_range — for packing slip
- fp.direct.order.line.thickness_range — for the wizard
- fp.part.catalog.x_fc_default_thickness_range — part default

AUTO-FILL CHAIN (sale.order.line + wizard line):
1. Operator already typed → keep
2. Most recent SO line for (this part, this customer) with a
   non-empty thickness_range → copy that
3. part.x_fc_default_thickness_range → copy
4. Blank — operator types

Implemented as both an @api.onchange (interactive) AND a
create() override (programmatic — wizard, sale_mrp bridge,
imports). Same logic in both paths.

WIZARD push-to-defaults: when "Save as Default" toggle is ticked
on a wizard line, persist the line's thickness_range to
part.x_fc_default_thickness_range so future first-customer orders
get a sensible starting point.

REPORTS: customer_line_header.xml + report_fp_wo_sticker.xml now
print the Char range as-typed (no display_name lookup needed).

KEPT (admin documentation only — doesn't affect order entry):
- recipe.thickness_min, thickness_max, thickness_uom on the recipe
  root: documents the recipe's CAPABILITY range. No UI gate; just
  for spec authors to record what the chemistry can produce.

JOB GROUPING: fp.job auto-create groups SO lines by (recipe, part,
spec, thickness, serial). Updated to key on the thickness_range
Char (stripped) instead of the deleted thickness_id integer.

DB cleanup: --update=base ran on the upgrade, dropping the
fp_recipe_thickness table + the four x_fc_thickness_id columns.
Existing data was already nulled in earlier dev work.

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

fusion_plating/fusion_plating/models/fp_process_node.py

@@ -357,13 +357,10 @@ class FpProcessNode(models.Model):
         [('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.',
-    )
+    # thickness_option_ids removed — fp.recipe.thickness model deleted.
+    # Thickness on the SO line is now a free-text Char range (e.g.
+    # "0.0005-0.0008 mils") that auto-fills from last-used per
+    # (part, customer) or the part's x_fc_default_thickness_range.
 
     # ---- Bake relief — AMS 2759/9 hydrogen embrittlement (recipe root) ----
     requires_bake_relief = fields.Boolean(