feat(plating): wire deferred UoM defaults — bake oven, bake window, coating, tank

Follow-up to the company-level UoM defaults commit. Wires four more
unit-bearing fields to inherit from res.company defaults at create-time.

**1. fp.bake.oven**
  • New `target_temp_uom` (°F / °C) — defaults from
    company.x_fc_default_temp_uom.
  • View: target_temp_min / max now render with a unit picker on the
    same row instead of unitless floats. Rule of thumb: "350–380 °F".

**2. fp.bake.window**
  • New `bake_temp_uom` — defaults from company.x_fc_default_temp_uom.
  • View: replaced hardcoded `°F` span with a live unit picker so the
    label matches whatever unit was actually recorded.

**3. fp.coating.config**
  • New `bake_temperature_uom` — defaults from company.
  • Removed hardcoded "Bake Temperature (°F)" label; the field is
    now unit-agnostic and the unit travels with the value.

**4. fp.tank.volume_uom**
  • Default now derives from company.x_fc_default_volume_uom via a
    small mapping (gal → gal_us, L → l, imp_gal → gal_imp). The
    selection itself stays the same — tanks already supported all
    common volume units; we just pre-pick the right one per company.

**Verified end-to-end** (scripts/fp_uom_smoke2.py):
  • Switching company default to °C + Litres
  • New oven gets C ✓
  • New bake window gets C ✓
  • New coating config gets C ✓
  • New tank gets `l` ✓ (mapped from company `L`)
  • Restored defaults afterwards

Existing records keep their stored uom — no surprise mutation.

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

fusion_plating/fusion_plating/models/fp_tank.py

@@ -72,7 +72,13 @@ class FpTank(models.Model):
             ('m3', 'Cubic metres'),
         ],
         string='Volume Unit',
-        default='l',
+        default=lambda self: {
+            'gal':     'gal_us',
+            'L':       'l',
+            'imp_gal': 'gal_imp',
+        }.get(self.env.company.x_fc_default_volume_uom or 'gal', 'gal_us'),
+        help='Inherited from company default (Settings → Fusion Plating → '
+             'Units of Measure). Overrideable per tank.',
     )
     material = fields.Selection(
         [