feat(configurator): Part cell rows 2-3 now editable — type to save

Customer feedback: rows 2 (description) and 3 (serials) in the Part
cell rendered as read-only spans. User wanted to edit directly.

New writable computed fields on fp.direct.order.line:
- part_name_editable: compute reads part_catalog_id.name, inverse
  writes back to part.name on the linked catalog record
- serials_text: compute joins serial_ids names with commas; inverse
  parses the typed string and find-or-creates fp.serial records,
  updates the line's serial_ids M2M

Removed the redundant rev separator (display_name already includes
'(Rev X)' so showing it twice was clutter). Rev edits happen by
editing the part record directly via the OPEN button.

OWL widget templates updated:
- Row 2: <input> bound to part_name_editable, t-on-change saves
- Row 3: <input> bound to serials_text, t-on-change parses + saves

SCSS:
- Row 2 input: italic, transparent border, focus tints background yellow
- Row 3 input: small grey text, comma-separated friendly placeholder
- Both disabled-look when no part is picked

Both inputs trigger the inverse method on blur. The G4 sync chain
takes over from there to push line.line_description etc. back to
the part as before — so editing in the line keeps the part defaults
fresh for future orders.

fusion_plating/fusion_plating_configurator/views/fp_express_order_views.xml

@@ -248,6 +248,10 @@
                             <field name="part_number_display" column_invisible="1"/>
                             <field name="part_revision_display" column_invisible="1"/>
                             <field name="part_name_display" column_invisible="1"/>
+                            <!-- Writable bridges used by the Part cell widget for
+                                 editable rows 2 (description) and 3 (serials). -->
+                            <field name="part_name_editable" column_invisible="1"/>
+                            <field name="serials_text" column_invisible="1"/>
                             <field name="serial_ids"
                                    widget="many2many_tags"
                                    options="{'no_quick_create': False, 'color_field': 'state_color'}"