feat(sticker): wire _qty_total in SO + Job External outers

Activates the per-box loop landed in the prior commit. SO External
reads line.product_uom_qty; Job External reads job.qty. Inner
template now renders one sticker per physical box, marking each
with "X / N" in the Qty row.

Verified on fp.job 2635 (qty temporarily set to 3): 3-page PDF
with Qty rows "1 / 3", "2 / 3", "3 / 3" — each page identical
otherwise (same WO#, same QR, same body fields).

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

fusion_plating/fusion_plating_jobs/report/report_fp_job_sticker.xml

@@ -60,6 +60,7 @@
                 <t t-set="_process" t-value="job.recipe_id or False"/>
                 <t t-set="_due" t-value="job.date_deadline or False"/>
                 <t t-set="_qty" t-value="job.qty"/>
+                <t t-set="_qty_total" t-value="job.qty"/>
                 <t t-set="_partner_name" t-value="job.partner_id.name"/>
                 <!-- The fp.job's own name (WH/JOB/00033) is already
                      printed in the header as "WO #...", so suppress