feat(fusion_accounting_reports): PDF export with QWeb template

Adds an AbstractModel report (report_pdf.py) and a single multi-purpose
QWeb template (report_pdf_template.xml) that renders P&L, Balance Sheet,
Trial Balance, and General Ledger results from the engine.

Wires the controller's /fusion/reports/export_pdf endpoint to actually
return base64-encoded PDF bytes via _render_qweb_pdf. The template walks
the result['rows'] list and applies indentation/bold based on level and
is_subtotal flags, with optional comparison columns when present.

Tests: 2 new (test_pdf_export.py) + 1 controller test updated to assert
the real PDF response. Net 109 -> 111.

Made-with: Cursor

fusion_accounting_reports/tests/test_reports_controller.py

@@ -101,13 +101,15 @@ class TestReportsController(HttpCase):
         self.assertIn('highlights', result)
         self.assertIn('concerns', result)
 
-    def test_export_pdf_placeholder(self):
+    def test_export_pdf_returns_pdf(self):
         result = self._jsonrpc('export_pdf', {
             'report_type': 'pnl',
             'date_from': '2026-01-01',
             'date_to': '2026-12-31',
         })
-        self.assertEqual(result.get('status'), 'not_implemented')
+        self.assertEqual(result.get('status'), 'ok')
+        self.assertIn('pdf_base64', result)
+        self.assertTrue(result.get('filename', '').endswith('.pdf'))
 
     def test_export_xlsx_placeholder(self):
         result = self._jsonrpc('export_xlsx', {