feat: expose codex-app-server version flag (#23593)

## Why

`codex-app-server` is published as a standalone release binary, so it
should support the same basic version inspection behavior users expect
from command-line tools. This is independent of package assembly:
package metadata now comes from `codex-rs/Cargo.toml`, but the
standalone app-server binary should still answer `--version` directly.

## What changed

- Enables Clap's generated `--version` flag for the `codex-app-server`
binary by adding `#[command(version)]` to its top-level parser.

## Verification

- Ran `cargo run -p codex-app-server --bin codex-app-server --
--version` and verified it prints `codex-app-server 0.0.0`.

codex-rs/app-server/src/main.rs

@@ -17,6 +17,7 @@ const MANAGED_CONFIG_PATH_ENV_VAR: &str = "CODEX_APP_SERVER_MANAGED_CONFIG_PATH"
 const DISABLE_MANAGED_CONFIG_ENV_VAR: &str = "CODEX_APP_SERVER_DISABLE_MANAGED_CONFIG";
 
 #[derive(Debug, Parser)]
+#[command(version)]
 struct AppServerArgs {
     /// Transport endpoint URL. Supported values: `stdio://` (default),
     /// `unix://`, `unix://PATH`, `ws://IP:PORT`, `off`.