feat(core): plumb distinct approval ids for command approvals (#12051)

zsh fork PR stack:
- https://github.com/openai/codex/pull/12051 👈 
- https://github.com/openai/codex/pull/12052

With upcoming support for a fork of zsh that allows us to intercept
`execve` and run execpolicy checks for each subcommand as part of a
`CommandExecution`, it will be possible for there to be multiple
approval requests for a shell command like `/path/to/zsh -lc 'git status
&& rg \"TODO\" src && make test'`.

To support that, this PR introduces a new `approval_id` field across
core, protocol, and app-server so that we can associate approvals
properly for subcommands.

codex-rs/app-server-protocol/src/protocol/v1.rs

@@ -258,6 +258,8 @@ pub struct ExecCommandApprovalParams {
     /// Use to correlate this with [codex_core::protocol::ExecCommandBeginEvent]
     /// and [codex_core::protocol::ExecCommandEndEvent].
     pub call_id: String,
+    /// Identifier for this specific approval callback.
+    pub approval_id: Option<String>,
     pub command: Vec<String>,
     pub cwd: PathBuf,
     pub reason: Option<String>,