feat(usage): show Zed plan quota on the dashboard

Add a Zed usage handler so connected Zed accounts appear on
/dashboard/quota. Reads GET /client/users/me for plan, edit
predictions, optional hosted model requests and billing-cycle reset.

Render unlimited rows as "N used · Unlimited" instead of 0 / ∞, and
surface overdue-invoice / token-billing messages.

open-sse/shared/zedAuth.js

@@ -172,8 +172,8 @@ function getSystemId(credentials) {
   );
 }
 
-async function fetchJson(url, options) {
-  const res = await proxyAwareFetch(url, options);
+async function fetchJson(url, options, proxyOptions = null) {
+  const res = await proxyAwareFetch(url, options, proxyOptions);
   const text = await res.text();
   let data = null;
   if (text) {
@@ -203,11 +203,15 @@ export async function fetchZedAuthenticatedUser(credentials, options = {}) {
   const systemId = getSystemId(credentials);
   if (systemId) headers[ZED_HEADERS.systemId] = systemId;
 
-  return fetchJson(zedUrl(config, "cloudBaseUrl", "/client/users/me", ZED_CLOUD_BASE_URL), {
-    method: "GET",
-    headers,
-    signal: options.signal ?? undefined,
-  });
+  return fetchJson(
+    zedUrl(config, "cloudBaseUrl", "/client/users/me", ZED_CLOUD_BASE_URL),
+    {
+      method: "GET",
+      headers,
+      signal: options.signal ?? undefined,
+    },
+    options.proxyOptions ?? null,
+  );
 }
 
 function normalizeOrganizationId(value) {