fix(usage): antigravity /usage display — dedupe by tier, fix account count, add projectId identity

- Antigravity usage provider now deduplicates model quota entries by tier
  instead of emitting one bar per model (15+ redundant bars for one account).
  The upstream API groups quota by tier — models within the same tier share
  the same quota bucket, so per-model bars were misleading noise.

- Reports now carry credential email and accountId in metadata so the
  /usage display and deduplicator can show meaningful account identities
  instead of 'account 1'.

- formatAggregateAmount no longer uses limits.length as account count.
  Instead counts unique accountId values from limit scopes — a single
  account's N incomplete limits no longer display as 'N accts'.

- Usage report dedup now considers metadata.projectId for Google Cloud
  providers so duplicate credential rows with the same project merge.

- account labels in both TUI and ACP markdown paths now fall back to
  metadata.projectId before the generic 'account N' placeholder.

packages/coding-agent/src/modes/controllers/command-controller.ts

@@ -1272,6 +1272,8 @@ function formatAccountLabel(limit: UsageLimit, report: UsageReport, index: numbe
 	if (email) return email;
 	const accountId = (report.metadata?.accountId as string | undefined) ?? limit.scope.accountId;
 	if (accountId) return accountId;
+	const projectId = report.metadata?.projectId as string | undefined;
+	if (projectId) return projectId;
 	return `account ${index + 1}`;
 }
 
@@ -1280,6 +1282,8 @@ function formatUnlimitedReportLabel(report: UsageReport, index: number): string
 	if (email) return email;
 	const accountId = report.metadata?.accountId as string | undefined;
 	if (accountId) return accountId;
+	const projectId = report.metadata?.projectId as string | undefined;
+	if (projectId) return projectId;
 	return `account ${index + 1}`;
 }
 
@@ -1365,7 +1369,12 @@ function formatAggregateAmount(limits: UsageLimit[]): string {
 		return `${formatNumber(remainingPct)}% free`;
 	}
 
-	return `${limits.length} accts`;
+	// Count unique accounts from limit scopes — not limits.length.
+	const uniqueAccountIds = new Set(
+		limits.map(limit => limit.scope.accountId).filter((id): id is string => typeof id === "string" && id.length > 0),
+	);
+	if (uniqueAccountIds.size === 0) return "";
+	return `${uniqueAccountIds.size} ${uniqueAccountIds.size === 1 ? "acct" : "accts"}`;
 }
 
 function resolveResetRange(limits: UsageLimit[], nowMs: number): string | null {