Rename exec_wait tool to wait (#14983)

Summary
- document that code mode only exposes `exec` and the renamed `wait`
tool
- update code mode tool spec and descriptions to match the new tool name
- rename tests and helper references from `exec_wait` to `wait`

Testing
- Not run (not requested)

codex-rs/core/src/features.rs

@@ -87,7 +87,7 @@ pub enum Feature {
     JsRepl,
     /// Enable a minimal JavaScript mode backed by Node's built-in vm runtime.
     CodeMode,
-    /// Restrict model-visible tools to code mode entrypoints (`exec`, `exec_wait`).
+    /// Restrict model-visible tools to code mode entrypoints (`exec`, `wait`).
     CodeModeOnly,
     /// Only expose js_repl tools directly to the model.
     JsReplToolsOnly,