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/OfferDetail.tsx

@@ -554,6 +554,10 @@ export default function OfferDetail() {
 
   const loading = isEdit && offerQuery.isLoading;
   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 [errors, setErrors] = useState<Record<string, string | undefined>>({});
   const [form, setForm] = useState<OfferForm>(emptyForm);
   const [items, setItems] = useState<OfferItem[]>(() => [emptyItem()]);
@@ -807,6 +811,7 @@ export default function OfferDetail() {
     if (Object.keys(newErrors).length > 0) return;
 
     setSaving(true);
+    setSavingAction(targetStatus ?? "save");
     try {
       const url = isEdit ? `${API_BASE}/offers/${id}` : `${API_BASE}/offers`;
       const payload: any = {
@@ -883,6 +888,7 @@ export default function OfferDetail() {
       alert.error("Chyba připojení");
     } finally {
       setSaving(false);
+      setSavingAction(null);
     }
   };
 
@@ -1136,7 +1142,7 @@ export default function OfferDetail() {
                   onClick={() => handleSave("draft")}
                   disabled={saving}
                 >
-                  {saving ? (
+                  {savingAction === "draft" ? (
                     <CircularProgress size={16} color="inherit" />
                   ) : (
                     "Uložit koncept"
@@ -1146,7 +1152,7 @@ export default function OfferDetail() {
                   onClick={() => handleSave(LIVE_STATUS)}
                   disabled={saving}
                 >
-                  {saving ? (
+                  {savingAction === LIVE_STATUS ? (
                     <>
                       <CircularProgress
                         size={16}
@@ -1171,7 +1177,7 @@ export default function OfferDetail() {
                   onClick={() => handleSave("draft")}
                   disabled={saving}
                 >
-                  {saving ? (
+                  {savingAction === "draft" ? (
                     <CircularProgress size={16} color="inherit" />
                   ) : (
                     "Uložit koncept"
@@ -1182,7 +1188,7 @@ export default function OfferDetail() {
                     onClick={() => handleSave(LIVE_STATUS)}
                     disabled={saving}
                   >
-                    {saving ? (
+                    {savingAction === LIVE_STATUS ? (
                       <>
                         <CircularProgress
                           size={16}
@@ -1202,7 +1208,7 @@ export default function OfferDetail() {
             {/* ── Edit mode, live (non-draft) offer — unchanged plain save ── */}
             {isEdit && !readOnly && offerStatus !== "draft" && (
               <Button onClick={() => handleSave()} disabled={saving}>
-                {saving ? (
+                {savingAction === "save" ? (
                   <>
                     <CircularProgress
                       size={16}