fix: allow generating review link for pre-existing posts

Show button only when post has no approval token. Once a link exists,
only the link is shown. Server preserves status for non-draft posts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/src/components/PostDetailPanel.jsx

@@ -436,7 +436,7 @@ export default function PostDetailPanel({ post, onClose, onSave, onDelete, brand
             {!isCreateMode && (
               <>
                 {/* Submit for Review */}
-                {(form.status === 'draft' || form.status === 'rejected') && (
+                {!reviewUrl && (
                   <button
                     onClick={handleSubmitReview}
                     disabled={submittingReview}