[mcp-server] Support CodexToolCallApprovalPolicy::OnRequest (#2187)

## Summary
#1865 added `AskForApproval::OnRequest`, but missed adding it to our
custom struct in `mcp-server`. This adds the missing configuration

## Testing
- [x] confirmed locally

codex-rs/mcp-server/src/codex_tool_config.rs

@@ -34,7 +34,7 @@ pub struct CodexToolCallParam {
     pub cwd: Option<String>,
 
     /// Approval policy for shell commands generated by the model:
-    /// `untrusted`, `on-failure`, `never`.
+    /// `untrusted`, `on-failure`, `on-request`, `never`.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub approval_policy: Option<CodexToolCallApprovalPolicy>,
 
@@ -63,6 +63,7 @@ pub struct CodexToolCallParam {
 pub enum CodexToolCallApprovalPolicy {
     Untrusted,
     OnFailure,
+    OnRequest,
     Never,
 }
 
@@ -71,6 +72,7 @@ impl From<CodexToolCallApprovalPolicy> for AskForApproval {
         match value {
             CodexToolCallApprovalPolicy::Untrusted => AskForApproval::UnlessTrusted,
             CodexToolCallApprovalPolicy::OnFailure => AskForApproval::OnFailure,
+            CodexToolCallApprovalPolicy::OnRequest => AskForApproval::OnRequest,
             CodexToolCallApprovalPolicy::Never => AskForApproval::Never,
         }
     }
@@ -244,10 +246,11 @@ mod tests {
             "type": "object",
             "properties": {
               "approval-policy": {
-                "description": "Approval policy for shell commands generated by the model: `untrusted`, `on-failure`, `never`.",
+                "description": "Approval policy for shell commands generated by the model: `untrusted`, `on-failure`, `on-request`, `never`.",
                 "enum": [
                   "untrusted",
                   "on-failure",
+                  "on-request",
                   "never"
                 ],
                 "type": "string"