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/common.rs

@@ -1003,6 +1003,7 @@ mod tests {
         let params = v1::ExecCommandApprovalParams {
             conversation_id,
             call_id: "call-42".to_string(),
+            approval_id: Some("approval-42".to_string()),
             command: vec!["echo".to_string(), "hello".to_string()],
             cwd: PathBuf::from("/tmp"),
             reason: Some("because tests".to_string()),
@@ -1022,6 +1023,7 @@ mod tests {
                 "params": {
                     "conversationId": "67e55044-10b1-426f-9247-bb680e5fe0c8",
                     "callId": "call-42",
+                    "approvalId": "approval-42",
                     "command": ["echo", "hello"],
                     "cwd": "/tmp",
                     "reason": "because tests",