Fix blob access mode for public store

The new Vercel Blob store is public, so private access is not allowed.
Switch cards read/write to public access.

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

apps/api/src/store.ts

@@ -25,7 +25,7 @@ export const storageMode = hasBlobToken() ? "Vercel Blob" : "Local file";
 export async function readCards(): Promise<BoardCard[]> {
   if (hasBlobToken()) {
     try {
-      const result = await get(dataBlobPath, { access: "private" });
+      const result = await get(dataBlobPath, { access: "public" });
       if (!result?.stream) {
         return [];
       }
@@ -52,7 +52,7 @@ export async function writeCards(cards: BoardCard[]) {
 
   if (hasBlobToken()) {
     await put(dataBlobPath, content, {
-      access: "private",
+      access: "public",
       contentType: "application/json",
       allowOverwrite: true
     });