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/protocol/src/approvals.rs

@@ -229,6 +229,16 @@ pub struct ExecApprovalRequestEvent {
     /// Uses `#[serde(default)]` for backwards compatibility.
     #[serde(default)]
     pub turn_id: String,
+    /// Environment in which the command will run.
+    #[serde(
+        default,
+        rename = "environmentId",
+        alias = "environment_id",
+        skip_serializing_if = "Option::is_none"
+    )]
+    #[ts(optional)]
+    #[ts(rename = "environmentId")]
+    pub environment_id: Option<String>,
     #[ts(type = "number")]
     pub started_at_ms: i64,
     /// The command to be executed.