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/path-key/index.js

@@ -0,0 +1,16 @@
+'use strict';
+
+const pathKey = (options = {}) => {
+	const environment = options.env || process.env;
+	const platform = options.platform || process.platform;
+
+	if (platform !== 'win32') {
+		return 'PATH';
+	}
+
+	return Object.keys(environment).reverse().find(key => key.toUpperCase() === 'PATH') || 'Path';
+};
+
+module.exports = pathKey;
+// TODO: Remove this for the next major release
+module.exports.default = pathKey;