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/merge-descriptors/index.js

@@ -0,0 +1,26 @@
+'use strict';
+
+function mergeDescriptors(destination, source, overwrite = true) {
+	if (!destination) {
+		throw new TypeError('The `destination` argument is required.');
+	}
+
+	if (!source) {
+		throw new TypeError('The `source` argument is required.');
+	}
+
+	for (const name of Object.getOwnPropertyNames(source)) {
+		if (!overwrite && Object.hasOwn(destination, name)) {
+			// Skip descriptor
+			continue;
+		}
+
+		// Copy descriptor
+		const descriptor = Object.getOwnPropertyDescriptor(source, name);
+		Object.defineProperty(destination, name, descriptor);
+	}
+
+	return destination;
+}
+
+module.exports = mergeDescriptors;