chore(playground): default gateway-local-shop to claude-opus-4-8

Switch the shop agent's default model to a Claude 4.6+ model so the playground
exercises the direct-Anthropic path (temperature drop-back + context-window
family default). Note: only takes effect in direct mode — remove the gateway
env vars for the AnthropicProvider path to run.

Co-Authored-By: claude-flow <ruv@ruv.net>

Author: tom-shyftlabs

playground/gateway-local-shop/config.py

@@ -44,7 +44,7 @@ class ShopConfig:
     agent_name: str = "shop-assistant"
     # Model name is sent as-is to the gateway — gateway routes to the provider.
     # Must be in the virtual key's allowed_models list (conf.json).
-    agent_model: str = "gpt-4o-mini"
+    agent_model: str = "claude-opus-4-8"
     agent_temperature: float = 0.7
     max_turns: int = 10