feat: add fusion_odoo_fixes module for default Odoo patches

- New standalone module to collect fixes for default Odoo behavior
- Fix #1: account_followup never clears followup_next_action_date
  when invoices are paid, causing collection emails to fully-paid
  clients. Hooks into _invoice_paid_hook to auto-clear stale data.
- Harden Fusion Accounting followup queries with amount_residual > 0
  filter and add balance check before sending emails

Co-authored-by: Cursor <cursoragent@cursor.com>

Fusion Accounting/wizard/followup_send_wizard.py

@@ -188,6 +188,15 @@ class FusionFollowupSendWizard(models.TransientModel):
         if not line:
             raise UserError(_("No follow-up record is linked to this wizard."))
 
+        line._compute_overdue_values()
+        if line.overdue_amount <= 0:
+            line.followup_status = 'no_action_needed'
+            raise UserError(_(
+                "Partner '%s' no longer has any overdue balance. "
+                "Follow-up cancelled.",
+                line.partner_id.display_name,
+            ))
+
         partner = line.partner_id
 
         # ---- Email ----