[IMP] tax_receipt_in_portal: pick report per company, hide missing PDFs

Replace the ``tax_receipt_in_portal.report_uuid`` system parameter by a
per-company setting, in Settings > Invoicing > Tax Receipts
(``res.company.tax_receipt_report_id``). Each receipt is rendered with
the report of its issuing company, not the current one: in the portal,
the current company is the website's. The selector only offers PDF Form
reports on ``l10n.fr.tax.receipt``; type and model are still checked at
rendering time since the report can be edited after selection.

The download buttons of the list and detail pages are only shown when
the PDF can actually be rendered: a valid report is configured for the
issuing company and no mapped field resolves to an empty value. The
checks are those of the rendering itself, exposed as a filter
(``_get_pdf_available_receipts``) and run in sudo to avoid false
negatives on field paths the donor cannot read. Otherwise a discreet
"PDF available soon" mention replaces the button, and the download URL
redirects to the receipt page.

The detail page download link now also carries the share token, so a
visitor reaching the page by token can download the PDF.

tax_receipt_in_portal/models/res_company.py

@@ -0,0 +1,29 @@
+# Copyright 2026 Elabore
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+"""Per-company choice of the report rendering tax receipts."""
+
+from odoo import fields, models
+
+#: Domain restricting the selectable reports to PDF Form reports on tax
+#: receipts. Shared by the company field and its settings counterpart.
+TAX_RECEIPT_REPORT_DOMAIN = (
+    "[('report_type', '=', 'pdf_form'),"
+    " ('model', '=', 'l10n.fr.tax.receipt'),"
+    " ('company_id', 'in', [False, {company}])]"
+)
+
+
+class ResCompany(models.Model):
+    """Store the tax receipt report of each issuing company."""
+
+    _inherit = "res.company"
+
+    tax_receipt_report_id = fields.Many2one(
+        "ir.actions.report",
+        string="Tax Receipt Report",
+        ondelete="set null",
+        domain=TAX_RECEIPT_REPORT_DOMAIN.format(company="id"),
+        help="PDF Form report used to render the tax receipts issued by "
+        "this company in the portal. Without it, donors can see their "
+        "receipts but not download them.",
+    )