feat(configurator): C1+C3 - pricelist currency picker + Express SCSS (light + dark)

C1: product.pricelist._compute_display_name override gated by the
'fp_express_currency_picker' context flag (set on the Express form's
pricelist_id field). When active, prefixes the dropdown label with
the currency code: 'CAD — Public Pricelist (CAD)'. Elsewhere the
standard display name is unchanged.

C3: SCSS tokens + base styles for the Express form. Tokens use the
compile-time @if $o-webclient-color-scheme branch per the project's
'Dark Mode' rule — same SCSS compiles into both bundles with different
hex values. Token vars wrapped in CSS custom properties so downstream
modules can override for per-shop branding without recompiling.
Base styles: spreadsheet-feel table borders, bake-cell inset-pill,
customer line ref bold/uppercase, accent section markers.

fusion_plating/fusion_plating_configurator/views/fp_express_order_views.xml

@@ -131,6 +131,7 @@
                         <group string="Pricing &amp; Fulfilment">
                             <field name="pricelist_id"
                                    string="Currency / Pricelist"
+                                   context="{'fp_express_currency_picker': True}"
                                    options="{'no_create_edit': True}"/>
                             <field name="payment_term_id"
                                    options="{'no_create': True}"/>