Add Windows hook command overrides (#22159)

# Why

Managed hook configs need a shared cross-platform shape without making
the existing `command` field polymorphic. The common case is still one
command string, with Windows needing a different entrypoint only when
the runtime is actually Windows.

Keeping `command` as the portable/default path and adding an optional
Windows override keeps the config easier to read, preserves the existing
scalar shape for non-Windows users, and avoids forcing every caller into
a `{ unix, windows }` object when only one platform needs special
handling.

# What

- Add optional `command_windows` / `commandWindows` alongside the
existing hook `command` field.
- Resolve `command_windows` only on Windows during hook discovery; other
platforms continue to use `command` unchanged.
- Keep trust hashing aligned to the effective command selected for the
current runtime.

# Docs

The Codex hooks/config reference should document `command_windows` as
the Windows-only override for command hooks.

codex-rs/app-server-protocol/src/protocol/v2/config.rs

@@ -413,6 +413,9 @@ pub enum ConfiguredHookHandler {
     #[ts(rename = "command")]
     Command {
         command: String,
+        #[serde(rename = "commandWindows")]
+        #[ts(rename = "commandWindows")]
+        command_windows: Option<String>,
         #[serde(rename = "timeoutSec")]
         #[ts(rename = "timeoutSec")]
         timeout_sec: Option<u64>,