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/tui/src/app/startup_prompts.rs

@@ -66,9 +66,9 @@ pub(super) fn emit_project_config_warnings(app_event_tx: &AppEventSender, config
 }
 
 pub(super) fn emit_system_bwrap_warning(app_event_tx: &AppEventSender, config: &Config) {
-    let Some(message) = crate::legacy_core::config::system_bwrap_warning(
-        config.permissions.permission_profile.get(),
-    ) else {
+    let Some(message) =
+        codex_sandboxing::system_bwrap_warning(config.permissions.permission_profile.get())
+    else {
         return;
     };