fix(loyalty-terminal): localise cooldown toast (was raw English)

When earn-points or add-stamp was rejected by the new cooldown
enforcement, the terminal showed the raw English error message from
the backend in the toast, even on FR / DE / LB locales:
  "Transaction failed: Please wait 15 minutes between point-earning..."

Two-part fix:

1. static/shared/js/api-client.js — when raising apiError on non-OK
   responses, also propagate the `details` payload from the response
   body (alongside the existing errorCode). Without this the catch
   sites had no structured access to e.g. cooldown_minutes.

2. loyalty-terminal.js — in the catch around the transaction dispatch,
   when error.errorCode is POINTS_COOLDOWN or STAMP_COOLDOWN, render a
   new localised key loyalty.store.terminal.cooldown_wait_minutes with
   {minutes} interpolated from error.details.cooldown_minutes (with a
   fallback to this.program.cooldown_minutes). Toast type switches to
   'warning' since the rejection is soft (try again later) rather than
   a hard failure. Other errors keep the existing 'transaction_failed'
   path so nothing else regresses.

Added the new key in en / fr / de / lb under the existing
loyalty.store.terminal.* namespace (sibling of the existing
cooldown_active label).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

static/shared/js/api-client.js

@@ -171,6 +171,10 @@ class APIClient {
                 const apiError = new Error(errorMessage);
                 apiError.status = response.status;
                 apiError.errorCode = data.error_code;
+                // Propagate the details payload so callers can localise the
+                // toast (e.g. "cooldown_ends" / "cooldown_minutes" for
+                // POINTS_COOLDOWN / STAMP_COOLDOWN).
+                apiError.details = data.details || null;
                 throw apiError;
             }