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/services/usage.js

@@ -14,6 +14,7 @@ import { getCodeBuddyCnUsage, getCodeBuddyIntlUsage } from "./usage/codebuddy-cn
 import { getGrokCliUsage } from "./usage/grok-cli.js";
 import { getKimiUsage } from "./usage/kimi.js";
 import { getDeepseekUsage } from "./usage/deepseek.js";
+import { getZedUsage } from "./usage/zed.js";
 import { resolveQoderCredentials } from "./qoderModels.js";
 import { getGlmUsage } from "./usage/glm.js";
 import {
@@ -54,6 +55,7 @@ const USAGE_HANDLERS = {
   "grok-cli": (c) => getGrokCliUsage(c.accessToken, c.providerSpecificData, c.proxyOptions),
   kimi: (c) => getKimiUsage(c.accessToken, c.apiKey, c.proxyOptions, c.providerSpecificData),
   deepseek: (c) => getDeepseekUsage(c.apiKey, c.proxyOptions),
+  zed: (c) => getZedUsage(c.accessToken, c.providerSpecificData, c.proxyOptions),
 };
 
 export async function getUsageForProvider(connection, proxyOptions = null, options = {}) {