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/v3/errors.d.cts

@@ -0,0 +1,5 @@
+import type { ZodErrorMap } from "./ZodError.cjs";
+import defaultErrorMap from "./locales/en.cjs";
+export { defaultErrorMap };
+export declare function setErrorMap(map: ZodErrorMap): void;
+export declare function getErrorMap(): ZodErrorMap;