Audit short-term: currency preview, date bounds, success destination, safe-area

- H3: Live currency preview below currency inputs shows the value formatted
  with thousands separators (en-US, USD) using Intl.NumberFormat. Skipped
  inside matrix cells to keep the Y1 monthly table compact.
- M1: Date inputs now apply min/max bounds. Default window is 1900-01-01 to
  2100-12-31; per-field override via FieldConfig.min/max as ISO strings.
- H6: On successful submit, replace the form with a SuccessDestination card
  (large checkmark, org name, "Submit another" + "safe to close" affordance).
  Prevents accidental duplicate submits from back-button / autofill replay.
- M6: Sticky submit bar respects iOS safe-area-inset-bottom.

FieldRenderer now takes a control prop so the currency preview can subscribe
to its single field via useWatch without re-rendering the whole form.

components/EngagementForm.tsx

@@ -182,6 +182,21 @@ export function EngagementForm({ config, cid, cs }: EngagementFormProps) {
   if (load.kind === "loading") return <LoadingState />;
   if (load.kind === "error") return <ErrorState message={load.message} />;
 
+  // After a successful submit, replace the form entirely with a destination
+  // screen. This prevents accidental duplicate submits (back-button, double-
+  // click, browser autofill replay) and gives the user a clear endpoint.
+  if (submitState.kind === "success") {
+    return (
+      <SuccessDestination
+        orgName={load.data.orgName}
+        onAnother={() => {
+          setSubmitState({ kind: "idle" });
+          window.scrollTo({ top: 0, behavior: "smooth" });
+        }}
+      />
+    );
+  }
+
   const onSubmit = async (values: Record<string, unknown>) => {
     setSubmitState({ kind: "submitting" });
     try {
@@ -283,6 +298,7 @@ export function EngagementForm({ config, cid, cs }: EngagementFormProps) {
               <StageSection
                 section={section}
                 register={register}
+                control={control}
                 errors={errors}
                 formValues={evalState}
                 isCurrent={section.rank === currentRank}
@@ -392,7 +408,10 @@ function SubmitBar({
   draftSavedAt: string | null;
 }) {
   return (
-    <div className="sticky bottom-3 z-20 flex flex-col gap-3 rounded-lg border border-rule bg-paper/95 px-5 py-4 shadow-[0_-4px_24px_-12px_rgba(60,80,40,0.2)] backdrop-blur sm:flex-row sm:items-center sm:justify-between sm:px-6">
+    <div
+      className="sticky bottom-3 z-20 flex flex-col gap-3 rounded-lg border border-rule bg-paper/95 px-5 py-4 shadow-[0_-4px_24px_-12px_rgba(60,80,40,0.2)] backdrop-blur sm:flex-row sm:items-center sm:justify-between sm:px-6"
+      style={{ marginBottom: "env(safe-area-inset-bottom)" }}
+    >
       <div className="flex flex-col gap-0.5">
         <SubmitFeedback state={state} />
         {state.kind === "idle" && (
@@ -429,12 +448,6 @@ function SubmitFeedback({ state }: { state: SubmitStatus }) {
         Saving your check-in…
       </p>
     );
-  if (state.kind === "success")
-    return (
-      <p className="text-sm font-medium text-leaf-800" role="status">
-        ✓ Check-in saved. Thank you.
-      </p>
-    );
   if (state.kind === "error")
     return (
       <p className="text-sm font-medium text-clay-700" role="alert">
@@ -471,6 +484,49 @@ function LoadingState() {
   );
 }
 
+function SuccessDestination({
+  orgName,
+  onAnother,
+}: {
+  orgName: string;
+  onAnother: () => void;
+}) {
+  return (
+    <section
+      role="status"
+      aria-live="polite"
+      className="rounded-lg border-2 border-leaf-600 bg-leaf-50/40 px-6 py-10 text-center shadow-[0_1px_0_0_rgba(0,0,0,0.04),0_12px_32px_-16px_rgba(60,80,40,0.22)] sm:px-10 sm:py-12"
+    >
+      <div
+        aria-hidden
+        className="mx-auto flex h-14 w-14 items-center justify-center rounded-full bg-leaf-700 text-paper shadow-sm"
+      >
+        <svg viewBox="0 0 24 24" className="h-7 w-7" fill="none" stroke="currentColor" strokeWidth="2.5" strokeLinecap="round" strokeLinejoin="round">
+          <path d="M5 12l5 5 9-11" />
+        </svg>
+      </div>
+      <h2 className="mt-5 font-display text-2xl font-medium leading-tight tracking-tight text-ink sm:text-3xl">
+        Check-in saved
+      </h2>
+      <p className="mx-auto mt-3 max-w-prose text-[15px] leading-relaxed text-ink-soft">
+        Thank you. We&apos;ve recorded this check-in for{" "}
+        <span className="font-medium text-ink">{orgName}</span>. Your engagement coordinator will see
+        it on their next review.
+      </p>
+      <div className="mt-7 flex flex-col items-center justify-center gap-3 sm:flex-row">
+        <button
+          type="button"
+          onClick={onAnother}
+          className="inline-flex items-center justify-center rounded-md border border-rule bg-paper px-5 py-2 text-sm font-medium text-ink-soft transition hover:bg-paper-2/60 focus:outline-none focus-visible:ring-2 focus-visible:ring-leaf-500/40"
+        >
+          Submit another check-in
+        </button>
+        <p className="text-xs text-ink-mute">It&apos;s safe to close this window.</p>
+      </div>
+    </section>
+  );
+}
+
 function ErrorState({ message }: { message: string }) {
   return (
     <div