feat(api): standardize errors as problem details

apps/web/src/lib/problem-response.ts

@@ -0,0 +1,16 @@
+import type { ProblemDetails } from "@minecraft-account-manager/contracts";
+
+export function problemInstance(request: Request) {
+  const url = new URL(request.url);
+  return `${url.pathname}${url.search}`;
+}
+
+export function problemResponse(problem: ProblemDetails) {
+  return new Response(JSON.stringify(problem), {
+    status: problem.status,
+    headers: {
+      "cache-control": "no-store",
+      "content-type": "application/problem+json",
+    },
+  });
+}