fix(ext/sw): atomic chrome.storage update in restore_backup

Single set({vaultConfig, imageBase64?}) instead of two sequential sets,
so a partial-write window can't leave vaultConfig pointing to the new
remote while imageBase64 still references the old vault.

extension/src/service-worker/router/popup-only.ts

@@ -483,10 +483,11 @@ export async function handle(
           repoPath: msg.newRemote.repoPath,
           apiToken: msg.newRemote.apiToken,
         };
-        await chrome.storage.local.set({ vaultConfig: cfg });
+        const storageUpdate: Record<string, unknown> = { vaultConfig: cfg };
         if (out.reference_jpg) {
-          await chrome.storage.local.set({ imageBase64: out.reference_jpg });
+          storageUpdate.imageBase64 = out.reference_jpg;
         }
+        await chrome.storage.local.set(storageUpdate);
 
         // Make sure the SW's gitHost cache picks up the new config.
         state.gitHost = newHost;