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/schema/json/ExecCommandApprovalParams.json

@@ -117,6 +117,13 @@
     }
   },
   "properties": {
+    "approvalId": {
+      "description": "Identifier for this specific approval callback.",
+      "type": [
+        "string",
+        "null"
+      ]
+    },
     "callId": {
       "description": "Use to correlate this with [codex_core::protocol::ExecCommandBeginEvent] and [codex_core::protocol::ExecCommandEndEvent].",
       "type": "string"