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/object-inspect/example/circular.js

@@ -0,0 +1,6 @@
+'use strict';
+
+var inspect = require('../');
+var obj = { a: 1, b: [3, 4] };
+obj.c = obj;
+console.log(inspect(obj));