fix(offers,invoices): per-button save loading state (only the clicked button spins)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/pages/InvoiceDetail.tsx

@@ -558,6 +558,10 @@ export default function InvoiceDetail() {
   ]);
   const [errors, setErrors] = useState<Record<string, string>>({});
   const [saving, setSaving] = useState(false);
+  // Which save action is in flight ("draft" | LIVE_STATUS | "save"), so only the
+  // clicked button shows its spinner — `saving` still disables all of them to
+  // prevent a concurrent double-submit.
+  const [savingAction, setSavingAction] = useState<string | null>(null);
   const [dataReady, setDataReady] = useState(false);
   const [invoiceNumber, setInvoiceNumber] = useState("");
   const initialSnapshotRef = useRef<string | null>(null);
@@ -976,6 +980,7 @@ export default function InvoiceDetail() {
     if (Object.keys(newErrors).length > 0) return;
 
     setSaving(true);
+    setSavingAction(targetStatus ?? "save");
     try {
       const payload: Record<string, unknown> = {
         ...form,
@@ -1016,6 +1021,7 @@ export default function InvoiceDetail() {
       );
     } finally {
       setSaving(false);
+      setSavingAction(null);
     }
   };
 
@@ -1710,7 +1716,7 @@ export default function InvoiceDetail() {
                   onClick={() => handleCreateSubmit("draft")}
                   disabled={saving}
                 >
-                  {saving ? (
+                  {savingAction === "draft" ? (
                     <CircularProgress size={16} color="inherit" />
                   ) : (
                     "Uložit koncept"
@@ -1720,7 +1726,7 @@ export default function InvoiceDetail() {
                   onClick={() => handleCreateSubmit(LIVE_STATUS)}
                   disabled={saving}
                 >
-                  {saving ? (
+                  {savingAction === LIVE_STATUS ? (
                     <>
                       <CircularProgress
                         size={16}
@@ -1745,7 +1751,7 @@ export default function InvoiceDetail() {
                   onClick={() => handleCreateSubmit("draft")}
                   disabled={saving}
                 >
-                  {saving ? (
+                  {savingAction === "draft" ? (
                     <CircularProgress size={16} color="inherit" />
                   ) : (
                     "Uložit koncept"
@@ -1756,7 +1762,7 @@ export default function InvoiceDetail() {
                     onClick={() => handleCreateSubmit(LIVE_STATUS)}
                     disabled={saving}
                   >
-                    {saving ? (
+                    {savingAction === LIVE_STATUS ? (
                       <>
                         <CircularProgress
                           size={16}
@@ -1787,7 +1793,7 @@ export default function InvoiceDetail() {
             {isEdit && invoice && invoice.status !== "draft" && (
               <>
                 <Button onClick={() => handleCreateSubmit()} disabled={saving}>
-                  {saving ? (
+                  {savingAction === "save" ? (
                     <>
                       <CircularProgress
                         size={16}