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-test-client/src/lib.rs

@@ -2058,6 +2058,7 @@ impl CodexClient {
             item_id,
             started_at_ms: _,
             approval_id,
+            environment_id,
             reason,
             network_approval_context,
             command,
@@ -2075,6 +2076,9 @@ impl CodexClient {
         );
         self.command_approval_count += 1;
         self.command_approval_item_ids.push(item_id.clone());
+        if let Some(environment_id) = environment_id.as_deref() {
+            println!("< environment: {environment_id}");
+        }
         if let Some(reason) = reason.as_deref() {
             println!("< reason: {reason}");
         }