feat(API-11): Route API calls through AgilitonAPI gateway

Add gateway-first pattern: when AGILITON_API_KEY is set, route all
external API calls through the gateway with X-API-Key auth. Falls back
to direct API access when gateway is unavailable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

node_modules/math-intrinsics/isInteger.js

@@ -0,0 +1,16 @@
+'use strict';
+
+var $abs = require('./abs');
+var $floor = require('./floor');
+
+var $isNaN = require('./isNaN');
+var $isFinite = require('./isFinite');
+
+/** @type {import('./isInteger')} */
+module.exports = function isInteger(argument) {
+	if (typeof argument !== 'number' || $isNaN(argument) || !$isFinite(argument)) {
+		return false;
+	}
+	var absValue = $abs(argument);
+	return $floor(absValue) === absValue;
+};