frontend: fix wallet push silently skipping in form dialogs

The "send to wallet" step in the appointment/invoice/prescription/
patient-edit/scribe dialogs was gated on sync.linked, which resolves
asynchronously via getWalletLink in an effect. A fast save (or a
transient failure that collapsed it to false) left a wallet-linked
patient looking unlinked, so the dialog took the else branch and pushed
nothing.

- Add ensureLinked() to useWalletSync: awaits getWalletLink at submit and
  returns the resolved status. Each of the 5 dialogs now awaits it before
  deciding whether to show the wallet step.
- Harden push() to drop empty/whitespace changes (the backend 400s on an
  empty change set) and add a translated summaryFallback so the step
  never sends an empty summary.

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

frontend/components/appointments/add-appointment-dialog.tsx

@@ -195,7 +195,7 @@ export function AddAppointmentDialog({
       t("appointments.dialog.addedTitle"),
       `${selected.name} · ${time}`,
     );
-    if (sync.linked) {
+    if (await sync.ensureLinked()) {
       setWalletSummary(
         t("walletSync.summary.appointment", { date: keyOf(date), time }),
       );