fix: add browserHttpEndpoint for client-side Apollo requests

The Apollo Client was using httpEndpoint (http://localhost:3000/api/graphql)
for browser requests, which fails on remote servers. Added browserHttpEndpoint
as relative URL "/api/graphql" so browser requests go to the correct origin.
Also added error logging to setInboxHidden mutation.

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

frontend/nuxt.config.ts

@@ -26,6 +26,7 @@ export default defineNuxtConfig({
     clients: {
       default: {
         httpEndpoint: process.env.GRAPHQL_HTTP_ENDPOINT || "http://localhost:3000/api/graphql",
+        browserHttpEndpoint: "/api/graphql",
         connectToDevTools: process.dev,
         httpLinkOptions: {
           credentials: "include",