feat(fusion_accounting_l10n_ca): Canadian reports + tax return tracking

Replaces Enterprise's l10n_ca_reports with Fusion-native equivalents:
- ca_balance_sheet, ca_profit_loss as fusion.report definitions
- fusion.tax.return model for GST/HST/PST/T4/T5018 filing tracking
- Auto-installs when l10n_ca + fusion_accounting_reports both present

Removes Westin's last Canadian-compliance dependency on Enterprise's
account_reports.

Made-with: Cursor

fusion_accounting_l10n_ca/models/__init__.py

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+from . import fusion_tax_return

fusion_accounting_l10n_ca/models/fusion_tax_return.py

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+"""Fusion-native tax return tracking.
+
+A simpler replacement for Enterprise's `account.return` model: a tax
+return is a (return_type, period_from, period_to, status) record. Filers
+mark them filed once submitted to CRA / Revenu Quebec / provincial
+authorities.
+"""
+
+from odoo import _, api, fields, models
+from odoo.exceptions import UserError
+
+
+class FusionTaxReturn(models.Model):
+    _name = "fusion.tax.return"
+    _inherit = ["mail.thread"]
+    _description = "Fusion Tax Return Filing"
+    _order = "date_to desc, id desc"
+
+    name = fields.Char(
+        string="Reference",
+        required=True,
+        copy=False,
+        index=True,
+        default=lambda self: _("New"),
+    )
+    return_type = fields.Selection(
+        [
+            ("gst_hst", "GST/HST Return"),
+            ("pst", "PST Return"),
+            ("qst", "QST Return"),
+            ("t4", "T4 Slip"),
+            ("t5018", "T5018 Statement"),
+            ("payroll_remittance", "Payroll Source Deductions"),
+            ("other", "Other"),
+        ],
+        required=True,
+        default="gst_hst",
+        tracking=True,
+    )
+
+    company_id = fields.Many2one(
+        "res.company",
+        required=True,
+        default=lambda self: self.env.company,
+    )
+    currency_id = fields.Many2one(related="company_id.currency_id")
+
+    date_from = fields.Date(string="Period Start", required=True)
+    date_to = fields.Date(string="Period End", required=True)
+
+    state = fields.Selection(
+        [
+            ("draft", "Draft"),
+            ("to_file", "To File"),
+            ("filed", "Filed"),
+            ("cancelled", "Cancelled"),
+        ],
+        default="draft",
+        required=True,
+        tracking=True,
+    )
+
+    filing_date = fields.Date(string="Filed On")
+    filing_reference = fields.Char(string="Confirmation #")
+    notes = fields.Text()
+
+    @api.model_create_multi
+    def create(self, vals_list):
+        for vals in vals_list:
+            if vals.get("name", _("New")) == _("New"):
+                vals["name"] = self.env["ir.sequence"].next_by_code(
+                    "fusion.tax.return"
+                ) or _("New")
+        return super().create(vals_list)
+
+    @api.constrains("date_from", "date_to")
+    def _check_period(self):
+        for r in self:
+            if r.date_from and r.date_to and r.date_from > r.date_to:
+                raise UserError(_("Period start must precede period end."))
+
+    def action_mark_filed(self):
+        self.ensure_one()
+        if self.state != "to_file":
+            raise UserError(_("Can only mark 'To File' returns as filed."))
+        self.write(
+            {
+                "state": "filed",
+                "filing_date": fields.Date.context_today(self),
+            }
+        )
+        return True