fix(ci): bump openapi.yaml version to 2.2.4

check:docs-sync fails when openapi.yaml version != package.json version.
Updating to match after v2.2.4 release.

Systematic fix: openapi.yaml version must always be updated alongside
package.json during releases (see generate-release workflow step 4).

docs/openapi.yaml

@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: OmniRoute API
-  version: 2.2.3
+  version: 2.2.4
   description: |
     OmniRoute is a local-first AI API proxy router. It provides an OpenAI-compatible
     endpoint that routes requests to multiple AI providers with load balancing,