Scope command approvals by execution environment (#28738)

## Why

Command approval cache keys included the command and working directory,
but not the execution environment. An approval for `/workspace` locally
could therefore be reused for the same command and path on an executor.

## What changed

- Include the selected environment ID in shell and unified-exec approval
cache keys.
- Carry that ID through the normal command approval request so clients
can show which environment is being approved.
- Expose the environment through app-server as a required nullable
`environmentId` and show it in the inline TUI approval prompt.
- Keep older recorded approval events compatible when the environment is
absent.

For example, `echo ok` in local `/workspace` and `echo ok` in executor
`/workspace` now produce different approval keys and separate prompts.

## Scope

This PR does not change network approvals, Guardian review actions, MCP
elicitation, full-screen TUI rendering, or environment-ID validation.
Remote `shell_command` execution itself remains in #28722; this PR only
makes its approval key environment-aware.

codex-rs/core/src/codex_delegate_tests.rs

@@ -322,6 +322,7 @@ async fn handle_exec_approval_uses_call_id_for_guardian_review_and_approval_id_f
                     call_id: "command-item-1".to_string(),
                     approval_id: Some("callback-approval-1".to_string()),
                     turn_id: "child-turn-1".to_string(),
+                    environment_id: Some("remote".to_string()),
                     started_at_ms: 0,
                     command: vec!["rm".to_string(), "-rf".to_string(), "tmp".to_string()],
                     cwd: test_path_buf("/tmp").abs(),