Trim TUI legacy core helper usage (#22695)

## Why

The TUI still had a few low-risk dependencies flowing through the
transitional `legacy_core` namespace after the app-server migration.
These helpers either already have clearer non-core owners or are
presentation logic that does not belong in `codex-core`, so moving them
out reduces the compatibility surface without changing product behavior.

## What changed

This is a low-risk change, almost completely mechanical in nature.

- Route TUI Codex-home lookup through `codex-utils-home-dir`, use
`Config::log_dir` directly, and call
`codex-sandboxing::system_bwrap_warning` without going through
`legacy_core`.
- Move shared `codex resume` hint formatting from `codex-core` into
`codex-utils-cli`.
- Update CLI and TUI call sites to use the shared CLI utility, and keep
the resume-command behavior covered by tests in its new home.

## Verification

- `cargo test -p codex-utils-cli`
- `cargo test -p codex-utils-cli resume_command`

codex-rs/Cargo.lock

@@ -3785,6 +3785,7 @@ dependencies = [
  "codex-protocol",
  "codex-realtime-webrtc",
  "codex-rollout",
+ "codex-sandboxing",
  "codex-shell-command",
  "codex-state",
  "codex-terminal-detection",
@@ -3794,6 +3795,7 @@ dependencies = [
  "codex-utils-cli",
  "codex-utils-elapsed",
  "codex-utils-fuzzy-match",
+ "codex-utils-home-dir",
  "codex-utils-oss",
  "codex-utils-path",
  "codex-utils-plugins",
@@ -3913,6 +3915,7 @@ version = "0.0.0"
 dependencies = [
  "clap",
  "codex-protocol",
+ "codex-shell-command",
  "pretty_assertions",
  "serde",
  "toml 0.9.11+spec-1.1.0",