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.

tests/unit/usage-dispatch.test.js

@@ -16,7 +16,7 @@ const SUPPORTED = [
   "github", "gemini-cli", "antigravity", "claude", "codex", "kiro",
   "qoder", "iflow", "ollama", "glm", "glm-cn",
   "minimax", "minimax-cn", "vercel-ai-gateway", "grok-cli", "kimi",
-  "deepseek",
+  "deepseek", "zed",
 ];
 
 describe("usage dispatch", () => {