fix(worker): trigger auto-topoff check on PTB insufficient balance errors

When PTB requests fail due to insufficient credits, the auto-topoff check
was never triggered because:
1. The checkAndScheduleAutoTopoffAlarm() call only existed in ProxyForwarder.ts
2. Failed escrow reservations returned early without reaching that code path

Now when escrow fails with "insufficient_credit_limit", we trigger the
auto-topoff alarm check. This ensures users with auto-topoff configured
will have their accounts recharged even when requests are being rejected.

Author: claude

worker/src/lib/ai-gateway/AttemptExecutor.ts

@@ -151,6 +151,15 @@ export class AttemptExecutor {
 
     const awaitedEscrow = await pendingEscrow;
     if (awaitedEscrow.error) {
+      // Trigger auto-topoff check when escrow fails due to insufficient credits
+      // This ensures auto-topoff can trigger even when requests are being rejected
+      if (awaitedEscrow.error.type === "insufficient_credit_limit") {
+        const walletId = this.env.WALLET.idFromName(props.orgId);
+        const walletStub = this.env.WALLET.get(walletId);
+        this.ctx.waitUntil(
+          walletStub.checkAndScheduleAutoTopoffAlarm(props.orgId)
+        );
+      }
       if (walletSpanId) {
         this.tracer.setError(walletSpanId, awaitedEscrow.error.message);
         this.tracer.finishSpan(walletSpanId);