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/models/followup.py

@@ -237,6 +237,7 @@ class FusionFollowupLine(models.Model):
                 ('account_id.account_type', '=', 'asset_receivable'),
                 ('parent_state', '=', 'posted'),
                 ('reconciled', '=', False),
+                ('amount_residual', '>', 0),
                 ('date_maturity', '<', today),
             ])
             line.overdue_amount = sum(overdue_lines.mapped('amount_residual'))
@@ -281,6 +282,8 @@ class FusionFollowupLine(models.Model):
         of the current follow-up level, then advances the partner to
         the next level.
 
+        Skips sending if the partner no longer has any overdue balance.
+
         :raises UserError: If no follow-up level is set.
         """
         self.ensure_one()
@@ -291,6 +294,11 @@ class FusionFollowupLine(models.Model):
                 self.partner_id.display_name,
             ))
 
+        self._compute_overdue_values()
+        if self.overdue_amount <= 0:
+            self.followup_status = 'no_action_needed'
+            return True
+
         level = self.followup_level_id
         partner = self.partner_id