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/nullable.js

@@ -0,0 +1,33 @@
+import { parseDef } from "../parseDef.js";
+import { primitiveMappings } from "./union.js";
+export function parseNullableDef(def, refs) {
+    if (["ZodString", "ZodNumber", "ZodBigInt", "ZodBoolean", "ZodNull"].includes(def.innerType._def.typeName) &&
+        (!def.innerType._def.checks || !def.innerType._def.checks.length)) {
+        if (refs.target === "openApi3") {
+            return {
+                type: primitiveMappings[def.innerType._def.typeName],
+                nullable: true,
+            };
+        }
+        return {
+            type: [
+                primitiveMappings[def.innerType._def.typeName],
+                "null",
+            ],
+        };
+    }
+    if (refs.target === "openApi3") {
+        const base = parseDef(def.innerType._def, {
+            ...refs,
+            currentPath: [...refs.currentPath],
+        });
+        if (base && "$ref" in base)
+            return { allOf: [base], nullable: true };
+        return base && { ...base, nullable: true };
+    }
+    const base = parseDef(def.innerType._def, {
+        ...refs,
+        currentPath: [...refs.currentPath, "anyOf", "0"],
+    });
+    return base && { anyOf: [base, { type: "null" }] };
+}