fix(api): resolve server-side relative URLs

lib/api/http.ts

@@ -38,6 +38,15 @@ export async function httpJson<T>(path: string, init?: JsonRequestInit): Promise
     throw new Error("Absolute URLs are not allowed")
   }
 
+  let url = path
+  if (
+    typeof window === "undefined" &&
+    path.startsWith("/") &&
+    process.env.NEXT_PUBLIC_BACKEND_URL
+  ) {
+    url = `${process.env.NEXT_PUBLIC_BACKEND_URL.replace(/\/$/, "")}${path}`
+  }
+
   const { json, headers: headersInit, body: bodyInit, ...rest } = init ?? {}
 
   const headers = new Headers(headersInit)
@@ -58,7 +67,7 @@ export async function httpJson<T>(path: string, init?: JsonRequestInit): Promise
     if (xsrfToken) headers.set("XSRF-TOKEN", xsrfToken)
   }
 
-  const res = await fetch(path, {
+  const res = await fetch(url, {
     ...rest,
     headers,
     body,