feat(admin): manual full-order refund + ledger CSV export

Closes the admin / reports / catalog work. Each fund row on the /_gm finance
panel gains a Refund action (payments.RefundOrderFull): a full-order refund the
operator records after refunding on the rail — a refund ledger row + a floor-0
chip revoke (never negative, D27), idempotent (a second refund reports
already-refunded). A ledger CSV export (/_gm/ledger.csv, payments.LedgerExport)
streams the whole append-only ledger for tax + reconciliation.

Tests: refund an order in full (chips revoked, a refund row), an idempotent
second refund, the CSV export shape; CSRF-guarded.

backend/internal/adminconsole/templates/pages/user_detail.gohtml

@@ -73,15 +73,18 @@
 </ul>
 {{else}}<p class="note">no balances or benefits</p>{{end}}
 <h3>Ledger</h3>
+{{$uid := .ID}}
 {{if .Finance.Ledger}}
 <table class="list">
-<thead><tr><th>Time</th><th>Kind</th><th>Source</th><th>Origin</th><th>Chips</th><th>Order</th><th>Provider</th><th>Detail</th></tr></thead>
+<thead><tr><th>Time</th><th>Kind</th><th>Source</th><th>Origin</th><th>Chips</th><th>Order</th><th>Provider</th><th>Detail</th><th></th></tr></thead>
 <tbody>
 {{range .Finance.Ledger}}
-<tr><td>{{.At}}</td><td>{{.Kind}}</td><td>{{.Source}}</td><td>{{.Origin}}</td><td>{{.ChipsDelta}}</td><td>{{if .Order}}<code>{{.Order}}</code>{{end}}</td><td>{{.Provider}}</td><td>{{if .Snapshot}}<code>{{.Snapshot}}</code>{{end}}</td></tr>
+<tr><td>{{.At}}</td><td>{{.Kind}}</td><td>{{.Source}}</td><td>{{.Origin}}</td><td>{{.ChipsDelta}}</td><td>{{if .Order}}<code>{{.Order}}</code>{{end}}</td><td>{{.Provider}}</td><td>{{if .Snapshot}}<code>{{.Snapshot}}</code>{{end}}</td>
+<td>{{if and (eq .Kind "fund") .Order}}<form class="form" method="post" action="/_gm/users/{{$uid}}/refund" onsubmit="return confirm('Refund this order in full? Record the money refund on the rail first; this revokes the chips (floored at 0).')"><input type="hidden" name="order_id" value="{{.Order}}"><button type="submit">Refund</button></form>{{end}}</td></tr>
 {{end}}
 </tbody>
 </table>
+<p class="note"><a href="/_gm/ledger.csv">Export the full ledger (CSV)</a> — all accounts, for tax + reconciliation.</p>
 {{else}}<p class="note">no ledger entries</p>{{end}}
 {{else}}<p class="note">payments not enabled</p>{{end}}
 </section>