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/mcp-server/src/codex_tool_runner.rs

@@ -220,6 +220,7 @@ async fn run_codex_tool_session_inner(
                         let approval_id = ev.effective_approval_id();
                         let ExecApprovalRequestEvent {
                             turn_id: _,
+                            environment_id: _,
                             started_at_ms: _,
                             command,
                             cwd,