feat(fusion_accounting_assets): asset category template model

- defaults applied to new assets (method, useful_life, declining rate,
  salvage %, prorate convention)
- GL account hooks: asset_account_id, depreciation_account_id,
  expense_account_id (domain-filtered to relevant account types)
- computed asset_count for kanban / list views
- 3 new tests (55 total)

Made-with: Cursor

fusion_accounting_assets/__manifest__.py

@@ -1,6 +1,6 @@
 {
     'name': 'Fusion Accounting Assets',
-    'version': '19.0.1.0.7',
+    'version': '19.0.1.0.8',
     'category': 'Accounting/Accounting',
     'summary': 'AI-augmented asset management with depreciation schedules.',
     'description': """