[daemon] Add app-server daemon lifecycle management (#20718)

## Why

Desktop and mobile Codex clients need a machine-readable way to
bootstrap and manage `codex app-server` on remote machines reached over
SSH. The same flow is also useful for bringing up app-server with
`remote_control` enabled on a fresh developer machine and keeping that
managed install current without requiring a human session.

## What changed

- add the new experimental `codex-app-server-daemon` crate and wire it
into `codex app-server daemon` lifecycle commands: `start`, `restart`,
`stop`, `version`, and `bootstrap`
- add explicit `enable-remote-control` and `disable-remote-control`
commands that persist the launch setting and restart a running managed
daemon so the change takes effect immediately
- emit JSON success responses for daemon commands so remote callers can
consume them directly
- support a Unix-only pidfile-backed detached backend for lifecycle
management
- assume the standalone `install.sh` layout for daemon-managed binaries
and always launch `CODEX_HOME/packages/standalone/current/codex`
- add bootstrap support for the standalone managed install plus a
detached hourly updater loop
- harden lifecycle management around concurrent operations, pidfile
ownership, stale state cleanup, updater ownership, managed-binary
preflight, Unix-only rejection, forced shutdown after the graceful
window, and updater process-group tracking/cleanup
- document the experimental Unix-only support boundary plus the
standalone bootstrap/update flow in
`codex-rs/app-server-daemon/README.md`

## Verification

- `cargo test -p codex-app-server-daemon -p codex-cli`
- live pid validation on `cb4`: `bootstrap --remote-control`, `restart`,
`version`, `stop`

## Follow-up

- Add updater self-refresh so the long-lived `pid-update-loop` can
replace its own executable image after installing a newer managed Codex
binary.

codex-rs/Cargo.toml

@@ -11,6 +11,7 @@ members = [
     "async-utils",
     "app-server",
     "app-server-transport",
+    "app-server-daemon",
     "app-server-client",
     "app-server-protocol",
     "app-server-test-client",
@@ -131,6 +132,7 @@ codex-api = { path = "codex-api" }
 codex-aws-auth = { path = "aws-auth" }
 codex-app-server = { path = "app-server" }
 codex-app-server-transport = { path = "app-server-transport" }
+codex-app-server-daemon = { path = "app-server-daemon" }
 codex-app-server-client = { path = "app-server-client" }
 codex-app-server-protocol = { path = "app-server-protocol" }
 codex-app-server-test-client = { path = "app-server-test-client" }