feat(app-server): persist remote-control desired state (#27445)

## Why

Remote-control runtime enablement and persisted enrollment preference
were represented by separate flags. That made startup rehydration, RPC
persistence, and new-enrollment seeding race with one another, and it
did not cleanly distinguish runtime-only CLI or daemon starts from
durable app-server RPC changes.

## What Changed

- Replace the parallel enablement, seed, and rehydration flags with one
transport-owned `RemoteControlDesiredState`.
- Add nullable enrollment-scoped persistence and preserve existing
preferences during enrollment upserts.
- Rehydrate plain startup only after auth and client scope resolve,
without overwriting a concurrent RPC transition.
- Make ordinary `remoteControl/enable` and `remoteControl/disable`
durable while retaining `ephemeral: true` for runtime-only callers.
- Have the daemon explicitly request ephemeral enablement and regenerate
the app-server schemas.

## Verification

- Covered migration and `NULL`/`0`/`1` persistence round trips.
- Covered plain-start rehydration and runtime-only versus durable
enrollment seeding.
- Covered durable enable, durable disable, and ephemeral enable through
app-server RPC.
- Covered the daemon's exact `{ "ephemeral": true }` request payload.

Related issue: N/A (internal remote-control persistence architecture
change).

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -864,13 +864,13 @@ client_request_definitions! {
     },
     #[experimental("remoteControl/enable")]
     RemoteControlEnable => "remoteControl/enable" {
-        params: #[ts(type = "undefined")] #[serde(skip_serializing_if = "Option::is_none")] Option<()>,
+        params: #[serde(skip_serializing_if = "Option::is_none")] v2::NullableRemoteControlEnableParams,
         serialization: global("remote-control"),
         response: v2::RemoteControlEnableResponse,
     },
     #[experimental("remoteControl/disable")]
     RemoteControlDisable => "remoteControl/disable" {
-        params: #[ts(type = "undefined")] #[serde(skip_serializing_if = "Option::is_none")] Option<()>,
+        params: #[serde(skip_serializing_if = "Option::is_none")] v2::NullableRemoteControlDisableParams,
         serialization: global("remote-control"),
         response: v2::RemoteControlDisableResponse,
     },