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/models/__init__.py

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+from . import fusion_report

fusion_accounting_reports/models/fusion_report.py

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+"""Persistent definition of a Fusion financial report.
+
+Each report (P&L, balance sheet, trial balance, GL) has ONE row in
+fusion.report describing its metadata + line specs. The line specs
+are stored as a JSON-typed field for flexibility (each line spec
+includes account_type filter, sub-totaling rules, sign convention)."""
+
+from odoo import _, api, fields, models
+
+
+REPORT_TYPES = [
+    ('pnl', 'Income Statement (P&L)'),
+    ('balance_sheet', 'Balance Sheet'),
+    ('trial_balance', 'Trial Balance'),
+    ('general_ledger', 'General Ledger'),
+]
+
+
+class FusionReport(models.Model):
+    _name = "fusion.report"
+    _description = "Fusion Financial Report Definition"
+    _order = "sequence, id"
+
+    name = fields.Char(required=True, translate=True)
+    code = fields.Char(
+        required=True,
+        help="Unique technical code (e.g. 'pnl', 'balance_sheet').",
+    )
+    report_type = fields.Selection(REPORT_TYPES, required=True)
+    sequence = fields.Integer(default=10)
+    description = fields.Text()
+    active = fields.Boolean(default=True)
+
+    # Layout config - stored as JSON for flexibility per report type.
+    # Example for P&L:
+    # [
+    #   {"label": "Revenue", "account_type_prefix": "income_", "sign": 1},
+    #   {"label": "Cost of Goods Sold", "account_type_prefix": "expense_direct_", "sign": -1},
+    #   {"label": "Gross Profit", "compute": "subtotal", "above": 2},
+    #   ...
+    # ]
+    line_specs = fields.Json(string="Line Specs")
+
+    show_zero_balances = fields.Boolean(default=False)
+    show_unposted = fields.Boolean(default=False)
+    default_comparison_mode = fields.Selection(
+        [
+            ('none', 'No comparison'),
+            ('previous_period', 'Previous Period'),
+            ('previous_year', 'Previous Year'),
+        ],
+        default='none',
+    )
+
+    company_id = fields.Many2one(
+        'res.company',
+        default=lambda self: self.env.company,
+    )
+
+    _unique_company_code = models.Constraint(
+        'UNIQUE(company_id, code)',
+        'Report code must be unique per company.',
+    )