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/app-server/tests/suite/v2/turn_start.rs

@@ -2067,6 +2067,7 @@ async fn turn_start_exec_approval_toggle_v2() -> Result<()> {
         panic!("expected CommandExecutionRequestApproval request");
     };
     assert_eq!(params.item_id, "call1");
+    assert_eq!(params.environment_id.as_deref(), Some("local"));
     let resolved_request_id = request_id.clone();
 
     // Approve and wait for task completion