fix(api): unbreak >10.6KB LLM requests and actually bind key-auth to the model routes

Two independent bugs, both silent, both found while pointing an agent harness
at api.riotpiao.com.

1. Requests over ~10.6KB failed with HTTP 400
   {"error":{"message":"[] is too short - 'messages'"}}.

   The request-transformer plugin on the llm-chat-* routes rewrites the JSON
   body, which means it reads it via kong.request.get_body(). That returns
   nothing once nginx spills the body past client_body_buffer_size into a temp
   file, so the plugin re-serialized a body with no `messages` and the upstream
   rejected it. Measured on /v1/ornith/chat/completions: 10588 B -> 200,
   11088 B -> 400. Isolated by size-sweeping /v1/embeddings, the one route with
   no request-transformer, which passed an 18057 B body straight through to a
   semantic 413 from TEI.

   Raises the Kong http-block buffer to 16m. Any agent request carrying tool
   schemas clears the old ceiling in a single turn.

2. key-auth was never applied to any model route.

   The model-key-auth KongPlugin sat in namespace `api` while all five routes
   that annotate it live in `llm-serving`. The ingress controller resolves
   konghq.com/plugins against the annotated object's own namespace, so the
   reference dangled and the plugin never bound. Verified before the fix:
   unauthenticated GET /v1/models and POST /v1/ornith/chat/completions both
   returned 200. A dangling plugin reference fails open and logs nothing.

   Re-test both without a key after this syncs; expect 401.

Note for follow-up: llm-embeddings and llm-score carry no plugins annotation at
all, so they stay unauthenticated even after this change.

Co-Authored-By: Claude Opus 5 <[email protected]>

k8s/apps/api/kong-values.yaml

@@ -57,6 +57,17 @@ env:
   # nginx Ingress in ingress.yaml; both hops have to be unbuffered or the
   # buffered one dominates.
   nginx_proxy_proxy_buffering: "off"
+  # Any plugin that rewrites the request body — request-transformer on the
+  # llm-chat-* routes — reads it through `kong.request.get_body()`, and that
+  # returns nothing once nginx has spilled the body past
+  # client_body_buffer_size into a temp file. The plugin then re-serializes a
+  # body with no `messages`, and the upstream answers
+  #   HTTP 400 {"error":{"message":"[] is too short - 'messages'"}}
+  # Measured on /v1/ornith/chat/completions: 10588 B -> 200, 11088 B -> 400.
+  # An agent request carrying tool schemas clears that in one turn, so the
+  # buffer has to hold a whole conversation, not a chat message.
+  nginx_http_client_body_buffer_size: "16m"
+  nginx_http_client_max_body_size: "16m"
 
 ingressController:
   enabled: true