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/function-bind/index.js

@@ -0,0 +1,5 @@
+'use strict';
+
+var implementation = require('./implementation');
+
+module.exports = Function.prototype.bind || implementation;