feat(jobs): finish original plan — Job Margin, polish, legacy hide

Three batched changes that close out the original 10-phase
migration plan.

1. Phase 5 — Job Margin report bound to fp.job (replaces the
   mrp.production-bound report_wo_margin). Per-step labour cost
   table + margin summary using existing fp.job.step.cost_total
   from Phase 1.

2. Polish:
   - Real implementations for fp.job.step.button_pause,
     button_skip, button_cancel (was NotImplementedError stubs).
     button_pause closes the open timelog and sums duration_actual,
     mirroring button_finish; button_skip/cancel transition state
     with UserError guards.
   - Explicit ondelete= policies on fp.job's cross-module Many2ones
     (part_catalog/coating restrict, customer_spec/portal/delivery
     set null) — was implicit set null.
   - Standard Nexa Systems author/website/maintainer/support block
     on fusion_plating_jobs manifest, suppressing the install
     warning.

3. Legacy hide:
   - New 'Plating Legacy Menus' group (group_fusion_plating_legacy_menus)
     — nobody in it by default.
   - Old shopfloor Manager Desk + Plant Overview + Tablet Station
     menus restricted to that group, hiding them from operators
     now that the native equivalents under 'Plating Jobs (Native)'
     exist. (Note: ir.ui.menu uses group_ids in Odoo 19, not the
     deprecated groups_id alias.)

Manifest 19.0.2.4.0 → 19.0.3.0.0. fusion_plating_shopfloor added
to depends so the legacy menu xmlid references resolve at install
time.

Part of: native job model migration (spec 2026-04-25)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating_jobs/models/__init__.py

@@ -6,6 +6,7 @@
 # task-by-task in Tasks 2.2 onwards.
 
 from . import fp_job
+from . import fp_job_step
 from . import fp_job_node_override
 from . import fp_portal_job
 from . import account_move
@@ -23,3 +24,6 @@ from . import fp_racking_inspection
 # Phase 4 — light refactors batch B (notifications, KPI source tag).
 from . import fp_notification_trigger
 from . import fusion_plating_kpi_value
+
+# Phase 5 — Job Margin report.
+from . import report_fp_job_margin