enable/disable remote control at runtime, not via features (#22578)

## Why
reapplies https://github.com/openai/codex/pull/22386 which was
previously reverted

Also, introduce `remoteControl/enable` and `remoteControl/disable`
app-server APIs to toggle on/off remote control at runtime for a given
running app-server instance.

## What Changed

- Adds experimental v2 RPCs:
  - `remoteControl/enable`
  - `remoteControl/disable`
- Adds `RemoteControlRequestProcessor` and routes the new RPCs through
it instead of `ConfigRequestProcessor`.
- Adds named `RemoteControlHandle::enable`, `disable`, and `status`
methods.
- Makes `remoteControl/enable` return an error when sqlite state DB is
unavailable, while keeping enrollment/websocket failures as async status
updates.
- Adds `AppServerRuntimeOptions.remote_control_enabled` and hidden
`--remote-control` flags for `codex app-server` and `codex-app-server`.
- Updates managed daemon startup to use `codex app-server
--remote-control --listen unix://`.
- Marks `Feature::RemoteControl` as removed and ignores
`[features].remote_control`.
- Updates app-server README entries for the new remote-control methods.

codex-rs/app-server-daemon/src/backend/pid.rs

@@ -349,13 +349,7 @@ impl PidBackend {
         match self.command_kind {
             PidCommandKind::AppServer {
                 remote_control_enabled: true,
-            } => vec![
-                "--enable",
-                "remote_control",
-                "app-server",
-                "--listen",
-                "unix://",
-            ],
+            } => vec!["app-server", "--remote-control", "--listen", "unix://"],
             PidCommandKind::AppServer {
                 remote_control_enabled: false,
             } => vec!["app-server", "--listen", "unix://"],

codex-rs/app-server-daemon/src/backend/pid_tests.rs

@@ -156,3 +156,17 @@ fn update_loop_uses_hidden_app_server_subcommand() {
         vec!["app-server", "daemon", "pid-update-loop"]
     );
 }
+
+#[test]
+fn app_server_remote_control_uses_runtime_flag() {
+    let backend = PidBackend::new(
+        "codex".into(),
+        "app-server.pid".into(),
+        /*remote_control_enabled*/ true,
+    );
+
+    assert_eq!(
+        backend.command_args(),
+        vec!["app-server", "--remote-control", "--listen", "unix://"]
+    );
+}