feat(uat-batch-20): form-error UX primitive — scroll-to-first-error hook + summary banner

Two new building blocks for the platform-wide form-error UX rework.
Expense form adopts both as the validation that the pattern works
before the broader sweep across the ~29 useForm callers.

- `useFormScrollToError(handleSubmit, errors)` — wraps RHF's
  handleSubmit. On validation failure it locates the first errored
  field via `[name="..."]` (or id fallback), walks ancestors to find
  the nearest scrolling container (key for forms inside Sheet /
  Dialog bodies that own their own overflow-y), and
  scrollTo({ behavior: 'smooth' }) + focus({ preventScroll }) on it.
  Type-loose handleSubmit signature so 2-arg and 3-arg useForm()
  callers (input vs transformed types) both work.
- `<FormErrorSummary errors={errors} labels={…}>` — top-of-form alert
  banner listing each failed field as a clickable anchor. Renders
  only when ≥2 errors (single-error case is handled by the hook
  alone). role="alert" aria-live="polite" for SR users.
- expense-form-dialog adopts both: `onSubmitWithScroll(onSubmit)`
  replaces the bare `handleSubmit(onSubmit)`, plus a labelled
  `<FormErrorSummary>` at the top of the form. Closes the loop on
  the silent-no-op zod-refine bug fixed in PR1 (the underlying
  setValue() fix already routes errors through formState; this
  surfaces them visibly).

tsc clean. 1419/1419 vitest pass.

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

src/components/forms/form-error-summary.tsx

@@ -0,0 +1,78 @@
+'use client';
+
+import { AlertCircle } from 'lucide-react';
+import type { FieldErrors, FieldValues } from 'react-hook-form';
+
+import { cn } from '@/lib/utils';
+
+interface FormErrorSummaryProps<TFieldValues extends FieldValues> {
+  errors: FieldErrors<TFieldValues>;
+  /**
+   * Optional override map for human-readable field labels. Falls back
+   * to the schema-supplied message label or the raw field name.
+   */
+  labels?: Partial<Record<keyof TFieldValues & string, string>>;
+  className?: string;
+}
+
+/**
+ * Top-of-form validation summary. Renders only when ≥2 fields have
+ * errors; a single-error form is handled by the
+ * `useFormScrollToError` hook (no banner needed). Each entry is an
+ * anchor link that scrolls + focuses the offending input on click.
+ */
+export function FormErrorSummary<TFieldValues extends FieldValues>({
+  errors,
+  labels,
+  className,
+}: FormErrorSummaryProps<TFieldValues>) {
+  const entries = Object.entries(errors).filter(([, err]) => err != null);
+  if (entries.length < 2) return null;
+
+  function onJump(name: string) {
+    const node =
+      (document.querySelector(`[name="${name}"]`) as HTMLElement | null) ??
+      (document.getElementById(name) as HTMLElement | null);
+    if (!node) return;
+    node.scrollIntoView({ block: 'center', behavior: 'smooth' });
+    if (typeof node.focus === 'function') {
+      window.setTimeout(() => node.focus({ preventScroll: true }), 50);
+    }
+  }
+
+  return (
+    <div
+      role="alert"
+      aria-live="polite"
+      className={cn(
+        'rounded-md border border-destructive/40 bg-destructive/5 px-3 py-2',
+        className,
+      )}
+    >
+      <div className="flex items-center gap-2 text-sm font-medium text-destructive">
+        <AlertCircle className="size-4" aria-hidden />
+        Please fix the following before submitting:
+      </div>
+      <ul className="mt-1.5 ml-6 list-disc text-xs text-destructive/90">
+        {entries.map(([name, err]) => {
+          const label =
+            (labels as Record<string, string> | undefined)?.[name] ??
+            (err && typeof err === 'object' && 'message' in err && typeof err.message === 'string'
+              ? err.message
+              : name);
+          return (
+            <li key={name}>
+              <button
+                type="button"
+                onClick={() => onJump(name)}
+                className="hover:underline focus:outline-none focus:underline"
+              >
+                {label}
+              </button>
+            </li>
+          );
+        })}
+      </ul>
+    </div>
+  );
+}