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/__manifest__.py

@@ -1,6 +1,6 @@
 {
     'name': 'Fusion Accounting Reports',
-    'version': '19.0.1.0.29',
+    'version': '19.0.1.0.30',
     'category': 'Accounting/Accounting',
     'summary': 'AI-augmented financial reports (P&L, balance sheet, trial balance, GL).',
     'description': """
@@ -36,6 +36,7 @@ menu hides; the engine and AI tools remain available for the chat.
         'data/report_trial_balance.xml',
         'data/report_general_ledger.xml',
         'data/cron.xml',
+        'reports/report_pdf_template.xml',
     ],
     'assets': {
         'web.assets_backend': [