[AI Assisted] Usage: add Google Antigravity usage tracking (#1490)

* Usage: add Google Antigravity usage tracking

- Add dedicated fetcher for google-antigravity provider
- Fetch credits and per-model quotas from Cloud Code API
- Report individual model IDs sorted by usage (top 10)
- Include comprehensive debug logging with [antigravity] prefix

* fix: refine antigravity usage tracking (#1490) (thanks @patelhiren)

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/infra/provider-usage.load.ts

@@ -1,5 +1,6 @@
 import { type ProviderAuth, resolveProviderAuths } from "./provider-usage.auth.js";
 import {
+  fetchAntigravityUsage,
   fetchClaudeUsage,
   fetchCodexUsage,
   fetchCopilotUsage,
@@ -57,8 +58,9 @@ export async function loadProviderUsageSummary(
             return await fetchClaudeUsage(auth.token, timeoutMs, fetchFn);
           case "github-copilot":
             return await fetchCopilotUsage(auth.token, timeoutMs, fetchFn);
-          case "google-gemini-cli":
           case "google-antigravity":
+            return await fetchAntigravityUsage(auth.token, timeoutMs, fetchFn);
+          case "google-gemini-cli":
             return await fetchGeminiUsage(auth.token, timeoutMs, fetchFn, auth.provider);
           case "openai-codex":
             return await fetchCodexUsage(auth.token, auth.accountId, timeoutMs, fetchFn);