feat(fusion_portal): Phase 1b - Assessment Visit model + accessibility funding grouping

Adds fusion.assessment.visit: the hub that bundles a home visit's assessments and,
on completion, groups its ACCESSIBILITY assessments by funding workflow
(x_fc_sale_type) and creates ONE draft sale order per workflow, reusing the existing
MOD/ODSP/etc. pipelines + the chatter-note pattern. ADP assessments keep one-SO-each
for now (ADP multi-device grouping is Phase 2).

- New model + sequence (VISIT/YYYY/NNNN) + ACL + backend list/form/menu.
- visit_id added to fusion.assessment, fusion.accessibility.assessment, sale.order.
- action_complete_visit() group-and-routes; MOD $15k cap + income-threshold flag
  surfaced (informational, no auto-enforcement).

NOT YET: completion-email consolidation; ADP multi-device (Phase 2); portal
add-as-you-go workspace (Phase 3). Untested locally (Enterprise knowledge dep) -
to be verified on a westin-v19 clone before prod.

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

fusion_portal/models/accessibility_assessment.py

@@ -157,7 +157,14 @@ class FusionAccessibilityAssessment(models.Model):
         readonly=True,
         copy=False,
     )
-    
+    visit_id = fields.Many2one(
+        'fusion.assessment.visit',
+        string='Assessment Visit',
+        ondelete='set null',
+        index=True,
+        help='The home visit this accessibility assessment belongs to.',
+    )
+
     # Dates
     assessment_date = fields.Date(
         string='Assessment Date',