Add request permissions tool (#13092)

Adds a built-in `request_permissions` tool and wires it through the
Codex core, protocol, and app-server layers so a running turn can ask
the client for additional permissions instead of relying on a static
session policy.

The new flow emits a `RequestPermissions` event from core, tracks the
pending request by call ID, forwards it through app-server v2 as an
`item/permissions/requestApproval` request, and resumes the tool call
once the client returns an approved subset of the requested permission
profile.

codex-rs/core/src/unified_exec/mod.rs

@@ -95,6 +95,7 @@ pub(crate) struct ExecCommandRequest {
     pub tty: bool,
     pub sandbox_permissions: SandboxPermissions,
     pub additional_permissions: Option<PermissionProfile>,
+    pub additional_permissions_preapproved: bool,
     pub justification: Option<String>,
     pub prefix_rule: Option<Vec<String>>,
 }
@@ -240,6 +241,7 @@ mod tests {
                     tty: true,
                     sandbox_permissions: SandboxPermissions::UseDefault,
                     additional_permissions: None,
+                    additional_permissions_preapproved: false,
                     justification: None,
                     prefix_rule: None,
                 },