fix: rename SetProviderRequest type

[nightcityblade]

Fixes #156

Summary

• rename the singular provider configuration request type from SetProvidersRequest to SetProviderRequest
• update the generated schema exports, zod schema, and ACP references to use the corrected name
• keep the request/response behavior unchanged while making the public type name match the docs

[benbrandt]

We need to fix upstream: agentclientprotocol/agent-client-protocol#1272
But thanks though!