[mcp-server] Update read config interface (#3093)

## Summary
Follow-up to #3056

This PR updates the mcp-server interface for reading the config settings
saved by the user. At risk of introducing _another_ Config struct, I
think it makes sense to avoid tying our protocol to ConfigToml, as its
become a bit unwieldy. GetConfigTomlResponse was a de-facto struct for
this already - better to make it explicit, in my opinion.

This is technically a breaking change of the mcp-server protocol, but
given the previous interface was introduced so recently in #2725, and we
have not yet even started to call it, I propose proceeding with the
breaking change - but am open to preserving the old endpoint.

## Testing
- [x] Added additional integration test coverage

codex-rs/core/src/config_profile.rs

@@ -22,3 +22,18 @@ pub struct ConfigProfile {
     pub chatgpt_base_url: Option<String>,
     pub experimental_instructions_file: Option<PathBuf>,
 }
+
+impl From<ConfigProfile> for codex_protocol::mcp_protocol::Profile {
+    fn from(config_profile: ConfigProfile) -> Self {
+        Self {
+            model: config_profile.model,
+            model_provider: config_profile.model_provider,
+            approval_policy: config_profile.approval_policy,
+            disable_response_storage: config_profile.disable_response_storage,
+            model_reasoning_effort: config_profile.model_reasoning_effort,
+            model_reasoning_summary: config_profile.model_reasoning_summary,
+            model_verbosity: config_profile.model_verbosity,
+            chatgpt_base_url: config_profile.chatgpt_base_url,
+        }
+    }
+}