chore: enusre the logic that creates ConfigLayerStack has access to cwd (#8353)

`load_config_layers_state()` should load config from a
`.codex/config.toml` in any folder between the `cwd` for a thread and
the project root. Though in order to do that,
`load_config_layers_state()` needs to know what the `cwd` is, so this PR
does the work to thread the `cwd` through for existing callsites.

A notable exception is the `/config` endpoint in app server for which a
`cwd` is not guaranteed to be associated with the query, so the `cwd`
param is `Option<AbsolutePathBuf>` to account for this case.

The logic to make use of the `cwd` will be done in a follow-up PR.

codex-rs/Cargo.lock

@@ -1154,6 +1154,7 @@ dependencies = [
  "codex-stdio-to-uds",
  "codex-tui",
  "codex-tui2",
+ "codex-utils-absolute-path",
  "codex-windows-sandbox",
  "ctor 0.5.0",
  "libc",