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/analytics/src/analytics_client_tests.rs

@@ -861,6 +861,7 @@ fn sample_command_approval_request(request_id: i64, approval_id: Option<&str>) -
             item_id: "item-1".to_string(),
             started_at_ms: 1_000,
             approval_id: approval_id.map(str::to_string),
+            environment_id: None,
             reason: None,
             network_approval_context: None,
             command: Some("echo hi".to_string()),