fix: locked offers — selects, checkboxes, date pickers, rich editor all read-only

Added isLockedByOther check to:
- All disabled={} on selects (currency, language) and checkboxes (apply_vat)
- All conditional renders that swap date pickers for read-only inputs
- Rich editor conditional that swaps editor for static HTML display

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/admin/pages/OfferDetail.tsx

@@ -769,7 +769,7 @@ export default function OfferDetail() {
 
           <div className="admin-form-row">
             <FormField label="Datum vytvoření" error={errors.created_at} required>
-              {isInvalidated ? (
+              {(isInvalidated || isLockedByOther) ? (
                 <input type="text" value={form.created_at} className="admin-form-input" readOnly />
               ) : (
                 <AdminDatePicker
@@ -783,7 +783,7 @@ export default function OfferDetail() {
               )}
             </FormField>
             <FormField label="Platnost do" error={errors.valid_until} required>
-              {isInvalidated ? (
+              {(isInvalidated || isLockedByOther) ? (
                 <input type="text" value={form.valid_until} className="admin-form-input" readOnly />
               ) : (
                 <AdminDatePicker
@@ -804,7 +804,7 @@ export default function OfferDetail() {
                 value={form.currency}
                 onChange={(e) => updateForm('currency', e.target.value)}
                 className="admin-form-select"
-                disabled={isInvalidated}
+                disabled={isInvalidated || isLockedByOther}
               >
                 <option value="EUR">EUR</option>
                 <option value="USD">USD</option>
@@ -817,7 +817,7 @@ export default function OfferDetail() {
                 value={form.language}
                 onChange={(e) => updateForm('language', e.target.value)}
                 className="admin-form-select"
-                disabled={isInvalidated}
+                disabled={isInvalidated || isLockedByOther}
               >
                 <option value="EN">English</option>
                 <option value="CZ">Čeština</option>
@@ -841,7 +841,7 @@ export default function OfferDetail() {
                     type="checkbox"
                     checked={form.apply_vat}
                     onChange={(e) => updateForm('apply_vat', e.target.checked)}
-                    disabled={isInvalidated}
+                    disabled={isInvalidated || isLockedByOther}
                   />
                   <span>Účtovat DPH</span>
                 </label>
@@ -1097,7 +1097,7 @@ export default function OfferDetail() {
 
                   <div style={{ marginTop: '0.5rem' }}>
                     <label className="admin-form-label">Obsah</label>
-                    {isInvalidated ? (
+                    {(isInvalidated || isLockedByOther) ? (
                       <div
                         className="admin-form-input"
                         style={{ minHeight: '80px', background: 'var(--bg-primary)' }}