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/res_partner_followup.py

@@ -76,7 +76,8 @@ class FusionPartnerFollowup(models.Model):
         """Return unpaid receivable move lines that are past due.
 
         Searches for posted, unreconciled journal items on receivable
-        accounts where the maturity date is earlier than today.
+        accounts where the maturity date is earlier than today and
+        there is still an outstanding balance.
 
         :returns: An ``account.move.line`` recordset.
         """
@@ -88,6 +89,7 @@ class FusionPartnerFollowup(models.Model):
             ('account_id.account_type', '=', 'asset_receivable'),
             ('parent_state', '=', 'posted'),
             ('reconciled', '=', False),
+            ('amount_residual', '>', 0),
             ('date_maturity', '<', today),
         ])