Remove simple TUI legacy_core reexports (#18631)

## Problem
The TUI still imported path utilities and config-loader symbols through
app-server-client's legacy_core facade even though those APIs already
exist in utility/config crates. This is part of our ongoing effort to
whittle away at these old dependencies.

## Solution
Rewire imports to avoid the TUI directly importing from the core crate
and instead import from common lower-level crates. This PR doesn't
include any functional changes; it's just a simple rewiring.

codex-rs/Cargo.lock

@@ -2999,6 +2999,7 @@ dependencies = [
  "codex-utils-elapsed",
  "codex-utils-fuzzy-match",
  "codex-utils-oss",
+ "codex-utils-path",
  "codex-utils-plugins",
  "codex-utils-pty",
  "codex-utils-sandbox-summary",