fix: eliminate blank overlay flash when opening ShareModal

Initialize hasRelationship and isCheckingRelationship based on whether
factoryId is present, so the first render frame already shows the correct
content instead of an empty backdrop overlay.

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

src/components/plans/ShareModal.tsx

@@ -66,8 +66,10 @@ export function ShareModal({
   const shortLinkGenerated = useRef(false);
   
   // 新流程状态
-  const [hasRelationship, setHasRelationship] = useState<boolean | null>(null);
-  const [isCheckingRelationship, setIsCheckingRelationship] = useState(false);
+  // When no factoryId (unlinked plan), we already know there's no relationship
+  // so initialize directly to avoid a blank-overlay flash before useEffect runs.
+  const [hasRelationship, setHasRelationship] = useState<boolean | null>(factoryId ? null : false);
+  const [isCheckingRelationship, setIsCheckingRelationship] = useState(!!factoryId);
   const [existingLink, setExistingLink] = useState<ShareLinkStatus | null>(null);
   const [isGeneratingLink, setIsGeneratingLink] = useState(false);
   const [pushSuccess, setPushSuccess] = useState(false);