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/CommandExecutionRequestApprovalParams.json

@@ -113,6 +113,13 @@
     }
   },
   "properties": {
+    "approvalId": {
+      "description": "Unique identifier for this specific approval callback.\n\nFor regular shell/unified_exec approvals, this is null.\n\nFor zsh-exec-bridge subcommand approvals, multiple callbacks can belong to one parent `itemId`, so `approvalId` is a distinct opaque callback id (a UUID) used to disambiguate routing.",
+      "type": [
+        "string",
+        "null"
+      ]
+    },
     "command": {
       "description": "The command to be executed.",
       "type": [