fix(mobile): restore images on repost, improve media library 404 error, null-safe stripHtml

- Pass post.image[] as JSON prefillImages param when prefilling compose from an existing post (repost/edit/retry), replacing the broken single-image prefillImagePath/prefillImageId approach
- MediaLibraryModal now shows the attempted URL and a clear explanation on 404, making it easier to diagnose if the Postiz version does not expose GET /media
- stripHtml accepts null/undefined input and returns "" instead of throwing

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

artifacts/postiz-mobile/app/(tabs)/compose.tsx

@@ -68,12 +68,11 @@ export default function ComposeScreen() {
   const insets = useSafeAreaInsets();
   const { workspaces, clients, isConfigured } = usePostiz();
   const queryClient = useQueryClient();
-  const { prefillContent, prefillIntegrationIds, prefillImagePath, prefillImageId } =
+  const { prefillContent, prefillIntegrationIds, prefillImages } =
     useLocalSearchParams<{
       prefillContent?: string;
       prefillIntegrationIds?: string;
-      prefillImagePath?: string;
-      prefillImageId?: string;
+      prefillImages?: string;
     }>();
 
   const [content, setContent] = useState("");
@@ -95,12 +94,23 @@ export default function ComposeScreen() {
     if (prefillIntegrationIds) {
       setSelectedChannels(String(prefillIntegrationIds).split(",").filter(Boolean));
     }
-    if (prefillImagePath && prefillImageId) {
-      // Prefilled image has unknown workspace; associate with first workspace
-      const wsId = workspaces[0]?.id ?? "";
-      setMediaItems([{ type: "uploaded", id: String(prefillImageId), path: String(prefillImagePath), workspaceId: wsId }]);
+    if (prefillImages && workspaces.length > 0) {
+      try {
+        const images: Array<{ id: string; path: string }> = JSON.parse(String(prefillImages));
+        const wsId = workspaces[0]?.id ?? "";
+        setMediaItems(
+          images
+            .filter((img) => img?.id && img?.path)
+            .map((img): MediaItem => ({
+              type: "uploaded",
+              id: img.id,
+              path: img.path,
+              workspaceId: wsId,
+            }))
+        );
+      } catch {}
     }
-  }, [prefillContent, prefillIntegrationIds, prefillImagePath, prefillImageId, workspaces]);
+  }, [prefillContent, prefillIntegrationIds, prefillImages, workspaces]);
 
   useEffect(() => {
     if (prefillContent) return;