fix: add missing env vars to render.yaml blueprint

Wire LLM_MODEL to the agent service and rate limiter env vars to the
frontend service so operators don't need to configure them manually
in the Render dashboard.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: GeneralJerel

render.yaml

@@ -11,6 +11,8 @@ services:
         sync: false
       - key: LANGSMITH_API_KEY
         sync: false
+      - key: LLM_MODEL
+        value: gpt-5.4-2026-03-05
     buildFilter:
       paths:
         - apps/agent/**
@@ -30,6 +32,12 @@ services:
           property: hostport
       - key: LANGSMITH_API_KEY
         sync: false
+      - key: RATE_LIMIT_ENABLED
+        value: "false"
+      - key: RATE_LIMIT_WINDOW_MS
+        value: "60000"
+      - key: RATE_LIMIT_MAX
+        value: "40"
     buildFilter:
       paths:
         - apps/app/**