Getting Started Hiccups

[nattaylor]

I faced some issues getting started.

• I send search products and I get error "Error: JSON-RPC error: Cannot read properties of undefined (reading 'messageId') (Code: -32603) Data: {}
• I used gpt-5-nano and got error "Error: 400 Unsupported value: 'temperature' does not support 0.3 with this model. Only the default (1) value is supported."
• I clicked "Search Products" and got Error: Tool execution failed: Tool not found: undefined

I propose to:

1. Fix the JSON-RPC error
2. Add per-model config with defaults for settings like temperature
3. Change "Search Products" to "Search Products Mock"

I will open a PR