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/app-server-protocol/src/protocol/v2/config.rs

@@ -381,6 +381,7 @@ pub struct ConfigRequirements {
     pub allowed_web_search_modes: Option<Vec<WebSearchMode>>,
     pub allow_managed_hooks_only: Option<bool>,
     pub allow_appshots: Option<bool>,
+    pub allow_remote_control: Option<bool>,
     pub computer_use: Option<ComputerUseRequirements>,
     pub feature_requirements: Option<BTreeMap<String, bool>>,
     #[experimental("configRequirements/read.hooks")]

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -1704,6 +1704,7 @@ fn config_requirements_granular_allowed_approval_policy_is_marked_experimental()
             allowed_web_search_modes: None,
             allow_managed_hooks_only: None,
             allow_appshots: None,
+            allow_remote_control: None,
             computer_use: None,
             feature_requirements: None,
             hooks: None,