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/ajv/lib/vocabularies/metadata.ts

@@ -0,0 +1,17 @@
+import type {Vocabulary} from "../types"
+
+export const metadataVocabulary: Vocabulary = [
+  "title",
+  "description",
+  "default",
+  "deprecated",
+  "readOnly",
+  "writeOnly",
+  "examples",
+]
+
+export const contentVocabulary: Vocabulary = [
+  "contentMediaType",
+  "contentEncoding",
+  "contentSchema",
+]