feat(tui): add /title terminal title configuration (#12334)

## Problem

When multiple Codex sessions are open at once, terminal tabs and windows
are hard to distinguish from each other. The existing status line only
helps once the TUI is already focused, so it does not solve the "which
tab is this?" problem.

This PR adds a first-class `/title` command so the terminal window or
tab title can carry a short, configurable summary of the current
session.

## Screenshot

<img width="849" height="320" alt="image"
src="https://github.com/user-attachments/assets/8b112927-7890-45ed-bb1e-adf2f584663d"
/>

## Mental model

`/statusline` and `/title` are separate status surfaces with different
constraints. The status line is an in-app footer that can be denser and
more detailed. The terminal title is external terminal metadata, so it
needs short, stable segments that still make multiple sessions easy to
tell apart.

The `/title` configuration is an ordered list of compact items. By
default it renders `spinner,project`, so active sessions show
lightweight progress first while idle sessions still stay easy to
disambiguate. Each configured item is omitted when its value is not
currently available rather than forcing a placeholder.

## Non-goals

This does not merge `/title` into `/statusline`, and it does not add an
arbitrary free-form title string. The feature is intentionally limited
to a small set of structured items so the title stays short and
reviewable.

This also does not attempt to restore whatever title the terminal or
shell had before Codex started. When Codex clears the title, it clears
the title Codex last wrote.

## Tradeoffs

A separate `/title` command adds some conceptual overlap with
`/statusline`, but it keeps title-specific constraints explicit instead
of forcing the status line model to cover two different surfaces.

Title refresh can happen frequently, so the implementation now shares
parsing and git-branch orchestration between the status line and title
paths, and caches the derived project-root name by cwd. That keeps the
hot path cheap without introducing background polling.

## Architecture

The TUI gets a new `/title` slash command and a dedicated picker UI for
selecting and ordering terminal-title items. The chosen ids are
persisted in `tui.terminal_title`, with `spinner` and `project` as the
default when the config is unset. `status` remains available as a
separate text item, so configurations like `spinner,status` render
compact progress like `⠋ Working`.

`ChatWidget` now refreshes both status surfaces through a shared
`refresh_status_surfaces()` path. That shared path parses configured
items once, warns on invalid ids once, synchronizes shared cached state
such as git-branch lookup, then renders the footer status line and
terminal title from the same snapshot.

Low-level OSC title writes live in `codex-rs/tui/src/terminal_title.rs`,
which owns the terminal write path and last-mile sanitization before
emitting OSC 0.

## Security

Terminal-title text is treated as untrusted display content before Codex
emits it. The write path strips control characters, removes invisible
and bidi formatting characters that can make the title visually
misleading, normalizes whitespace, and caps the emitted length.

References used while implementing this:

- [xterm control
sequences](https://invisible-island.net/xterm/ctlseqs/ctlseqs.html)
- [WezTerm escape sequences](https://wezterm.org/escape-sequences.html)
- [CWE-150: Improper Neutralization of Escape, Meta, or Control
Sequences](https://cwe.mitre.org/data/definitions/150.html)
- [CERT VU#999008 (Trojan Source)](https://kb.cert.org/vuls/id/999008)
- [Trojan Source disclosure site](https://trojansource.codes/)
- [Unicode Bidirectional Algorithm (UAX
#9)](https://www.unicode.org/reports/tr9/)
- [Unicode Security Considerations (UTR
#36)](https://www.unicode.org/reports/tr36/)

## Observability

Unknown configured title item ids are warned about once instead of
repeatedly spamming the transcript. Live preview applies immediately
while the `/title` picker is open, and cancel rolls the in-memory title
selection back to the pre-picker value.

If terminal title writes fail, the TUI emits debug logs around set and
clear attempts. The rendered status label intentionally collapses richer
internal states into compact title text such as `Starting...`, `Ready`,
`Thinking...`, `Working...`, `Waiting...`, and `Undoing...` when
`status` is configured.

## Tests

Ran:

- `just fmt`
- `cargo test -p codex-tui`

At the moment, the red Windows `rust-ci` failures are due to existing
`codex-core` `apply_patch_cli` stack-overflow tests that also reproduce
on `main`. The `/title`-specific `codex-tui` suite is green.

codex-rs/core/config.schema.json

@@ -1670,6 +1670,14 @@
           },
           "type": "array"
         },
+        "terminal_title": {
+          "default": null,
+          "description": "Ordered list of terminal title item identifiers.\n\nWhen set, the TUI renders the selected items into the terminal window/tab title. When unset, the TUI defaults to: `spinner` and `project`.",
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
+        },
         "theme": {
           "default": null,
           "description": "Syntax highlighting theme name (kebab-case).\n\nWhen set, overrides automatic light/dark theme detection. Use `/theme` in the TUI or see `$CODEX_HOME/themes` for custom themes.",