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/v2/remote_control.rs

@@ -3,6 +3,26 @@ use serde::Deserialize;
 use serde::Serialize;
 use ts_rs::TS;
 
+#[derive(Serialize, Deserialize, Debug, Clone, Default, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct RemoteControlEnableParams {
+    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+    pub ephemeral: bool,
+}
+
+pub type NullableRemoteControlEnableParams = Option<RemoteControlEnableParams>;
+
+#[derive(Serialize, Deserialize, Debug, Clone, Default, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct RemoteControlDisableParams {
+    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+    pub ephemeral: bool,
+}
+
+pub type NullableRemoteControlDisableParams = Option<RemoteControlDisableParams>;
+
 /// Current remote-control connection status and remote identity exposed to clients.
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]