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/has-symbols/index.js

@@ -0,0 +1,14 @@
+'use strict';
+
+var origSymbol = typeof Symbol !== 'undefined' && Symbol;
+var hasSymbolSham = require('./shams');
+
+/** @type {import('.')} */
+module.exports = function hasNativeSymbols() {
+	if (typeof origSymbol !== 'function') { return false; }
+	if (typeof Symbol !== 'function') { return false; }
+	if (typeof origSymbol('foo') !== 'symbol') { return false; }
+	if (typeof Symbol('bar') !== 'symbol') { return false; }
+
+	return hasSymbolSham();
+};