feat(fusion_plating): box-level tracking (fp.box) + thermal job-sticker redesign

Box registry: new fp.box model (fusion_plating_receiving), one record per
received box, auto-created when a receiving is marked Counted (idempotent
_fp_sync_boxes — grows/shrinks with box_count_in, never touches an advanced
box). Status received -> racked -> in_process -> packed -> shipped, per-box
scannable QR (/fp/box/<id> controller). Backfill migration for receivings
counted before tracking shipped. Boxes list/kanban/form + receiving smart
button.

Job stickers redesigned (thermal label, 6x4 in / 152x102mm, mm layout @
paperformat dpi=96 so mm maps 1:1 in wkhtmltopdf — see rule 14):
- Internal Job Sticker = Layout A, ONE per job (shop notes from
  x_fc_internal_description, job QR).
- External Job Sticker = Layout B, ONE per fp.box (BOX n/N, per-box QR,
  factory company logo, customer-facing notes). Dynamic MASK badge
  (x_fc_masking_enabled) + BAKE block (x_fc_bake_instructions), length-tiered
  notes font. Display logic in fp.job._fp_sticker_data().

Also retains the SO/WO box-sticker MemoryError fix in report_fp_wo_sticker.xml
(per-box loop sourced from fp.receiving.box_count_in + 100-label safety cap).

Verified live on entech: 111 boxes backfilled (31 receivings), External renders
one page per box, Internal one per job, scan endpoint 303->login.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating_receiving/views/fp_receiving_views.xml

@@ -125,6 +125,15 @@
                             </div>
                             <field name="x_fc_has_label_zpl" invisible="1"/>
                         </button>
+                        <button name="action_view_boxes"
+                                type="object"
+                                class="oe_stat_button"
+                                icon="fa-cubes"
+                                invisible="box_count_tracked == 0">
+                            <field name="box_count_tracked"
+                                   widget="statinfo"
+                                   string="Boxes"/>
+                        </button>
                     </div>
                     <div class="alert alert-info" role="alert">
                         <i class="fa fa-info-circle me-2"/>