dlv_account_reconciliation_rest_amount: rest op eigen regel + scope verduidelijkt

- Toon het restbedrag als "(rest: € ...)" op een eigen regel boven het
  ingezette bedrag i.p.v. inline ernaast.
- Manifest summary/description, README (nieuwe Scope-sectie) en CHANGELOG
  aangescherpt: addon dekt enkel gedeeltelijk afgepunte facturen; de
  bankbewegingsregel en het betalingsoverschot (open balance) zijn buiten
  scope.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dlv_account_reconciliation_rest_amount/README.md

@@ -20,6 +20,22 @@ remains unmatched on that line. This addon adds that missing number, e.g.:
 so the user immediately sees that €2.586,38 of that invoice is still
 outstanding, without having to search for it elsewhere.
 
+## Scope
+
+This addon covers exactly one case: an added invoice/bill line that is only
+**partially** used to close the statement line (invoice amount > amount used).
+The number shown is that invoice's residual / still-open amount
+(`amount_residual`, "restbedrag / openstaand saldo").
+
+Explicitly **out of scope**:
+
+- The bank movement (liquidity) line — always reflects the full statement line
+  amount; there is no partial/rest concept for it (see note below).
+- The opposite case, where the payment is *larger* than the matched invoice(s)
+  and the surplus is auto-posted to the suspense/waiting account as an "open
+  balance" line. That surplus is a property of the statement line, not of a
+  partially used invoice, so this addon does not annotate it.
+
 ## How it works
 
 - `models/bank_rec_widget_line.py` inherits `bank.rec.widget.line` and adds