feat(fusion_accounting_reports): fusion.report definition model

Persistent definition of a Fusion financial report. Each report (P&L,
balance sheet, trial balance, GL) has one row in fusion.report holding
its metadata + line specs (stored as JSON for layout flexibility).

V19 conventions: models.Constraint inline, no _sql_constraints. Per-
company uniqueness on (company_id, code).

3 new tests, 27 total passing.

Made-with: Cursor

fusion_accounting_reports/__manifest__.py

@@ -1,6 +1,6 @@
 {
     'name': 'Fusion Accounting Reports',
-    'version': '19.0.1.0.0',
+    'version': '19.0.1.0.1',
     'category': 'Accounting/Accounting',
     'summary': 'AI-augmented financial reports (P&L, balance sheet, trial balance, GL).',
     'description': """