feat(app-server): enforce managed remote control disable (#27961)

## Why

Managed deployments need a reliable deny gate for remote control.
Persisted enablement and explicit startup requests currently remain able
to start the transport, while the removed `features.remote_control` key
is intentionally only a compatibility no-op.

This adds a dedicated requirement that administrators can use to force
remote control off without deleting the user's persisted preference.
Removing the requirement and restarting restores the prior choice.

## What Changed

- Added top-level `allow_remote_control` requirements parsing, sourced
layer precedence, debug output, and `configRequirements/read` exposure
as `allowRemoteControl`.
- Added a typed transport policy captured from the startup requirements
snapshot. Managed disable forces the initial state to disabled and
prevents enrollment, refresh, connection, and persisted-preference
mutation.
- Rejected every `remoteControl/*` RPC before parameter deserialization
with JSON-RPC `-32600` and `remote control is disabled by managed
requirements`.
- Preserved the existing disabled status notification and the previous
behavior when the requirement is `true` or omitted.
- Regenerated app-server protocol schemas and documented the new
requirement.

## Verification

- Confirmed all remote-control RPCs, including a malformed request,
return the managed-policy error while the initial status notification
remains `disabled`.
- Confirmed explicit ephemeral startup and persisted enablement make no
backend connection and leave the SQLite preference unchanged.
- Confirmed `allow_remote_control = true` does not enable or block
remote control and `configRequirements/read` returns
`allowRemoteControl: false` for the deny policy.

Related issue: N/A (managed-policy hardening).

codex-rs/config/src/requirements_layers/stack.rs

@@ -182,6 +182,7 @@ fn populate_merged_regular_fields_with_sources(
         allowed_web_search_modes,
         allow_managed_hooks_only,
         allow_appshots,
+        allow_remote_control,
         computer_use,
         windows,
         feature_requirements,
@@ -210,6 +211,7 @@ fn populate_merged_regular_fields_with_sources(
     set_sourced!(allowed_web_search_modes, &["allowed_web_search_modes"]);
     set_sourced!(allow_managed_hooks_only, &["allow_managed_hooks_only"]);
     set_sourced!(allow_appshots, &["allow_appshots"]);
+    set_sourced!(allow_remote_control, &["allow_remote_control"]);
     set_sourced!(computer_use, &["computer_use"]);
     set_sourced!(windows, &["windows"]);
     set_sourced!(feature_requirements, &["features", "feature_requirements"]);