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/zod-to-json-schema/dist/esm/parsers/undefined.js

@@ -0,0 +1,6 @@
+import { parseAnyDef } from "./any.js";
+export function parseUndefinedDef(refs) {
+    return {
+        not: parseAnyDef(refs),
+    };
+}