feat(inbounds): clearer client validation errors on save

When an inbound save fails Zod validation, the toast previously showed a
raw path like `settings.clients.494.tgId: Invalid input`, which gave no
hint which of hundreds of clients was at fault. Resolve the client array
index back to the client email, name the field, and append a "(+N more)"
count when several fields fail. console.error now logs a readable list of
every issue instead of dumping the whole form.

Adds the invalidClientField/invalidField/moreIssues toast strings across
all 13 translations.

frontend/src/pages/inbounds/form/formatValidationError.ts

@@ -0,0 +1,43 @@
+import type { TFunction } from 'i18next';
+
+type IssueLike = { path: PropertyKey[]; message: string };
+
+interface ClientLike {
+  email?: unknown;
+}
+
+/**
+ * Turns one Zod issue from the inbound-form schema into a human-readable line.
+ * The schema validates the whole form at once, so a bad client field surfaces
+ * as `settings.clients.<index>.<field>` — useless on its own when an inbound
+ * holds hundreds of clients. We resolve that index back to the client's email
+ * so the operator can find the offending entry. The reason is translated when
+ * it is a custom message key; Zod defaults like "Invalid input" pass through.
+ */
+export function formatInboundIssue(issue: IssueLike, values: unknown, t: TFunction): string {
+  const path = Array.isArray(issue?.path) ? issue.path : [];
+  const reason = t(issue?.message, { defaultValue: issue?.message });
+
+  if (path[0] === 'settings' && path[1] === 'clients' && typeof path[2] === 'number') {
+    const index = path[2];
+    const clients = (values as { settings?: { clients?: ClientLike[] } })?.settings?.clients;
+    const client = Array.isArray(clients) ? clients[index] : undefined;
+    const email = typeof client?.email === 'string' && client.email !== '' ? client.email : '';
+    const who = email ? `"${email}"` : `#${index}`;
+    const field = path.slice(3).map(String).join('.') || t('clients');
+    return t('pages.inbounds.toasts.invalidClientField', { client: who, field, reason });
+  }
+
+  const field = path.map(String).join('.') || 'value';
+  return t('pages.inbounds.toasts.invalidField', { field, reason });
+}
+
+/**
+ * Builds the single-line toast for a failed inbound save: the first issue,
+ * fully described, plus a "(+N more)" tail when several fields failed.
+ */
+export function formatInboundValidation(issues: IssueLike[], values: unknown, t: TFunction): string {
+  const first = formatInboundIssue(issues[0], values, t);
+  if (issues.length <= 1) return first;
+  return t('pages.inbounds.toasts.moreIssues', { message: first, count: issues.length - 1 });
+}