feat(tui): add terminal title support to tui app server (#15860)

## TR;DR

Replicates the `/title` command from `tui` to `tui_app_server`.

## Problem

The classic `tui` crate supports customizing the terminal window/tab
title via `/title`, but the `tui_app_server` crate does not. Users on
the app-server path have no way to configure what their terminal title
shows (project name, status, spinner, thread, etc.), making it harder to
identify Codex sessions across tabs or windows.

## Mental model

The terminal title is a *status surface* -- conceptually parallel to the
footer status line. Both surfaces are configurable lists of items, both
share expensive inputs (git branch lookup, project root discovery), and
both must be refreshed at the same lifecycle points. This change ports
the classic `tui`'s design verbatim:

1. **`terminal_title.rs`** owns the low-level OSC write path and input
sanitization. It strips control characters and bidi/invisible codepoints
before placing untrusted text (model output, thread names, project
paths) inside an escape sequence.

2. **`title_setup.rs`** defines `TerminalTitleItem` (the 8 configurable
items) and `TerminalTitleSetupView` (the interactive picker that wraps
`MultiSelectPicker`).

3. **`status_surfaces.rs`** is the shared refresh pipeline. It parses
both surface configs once per refresh, warns about invalid items once
per session, synchronizes the git-branch cache, then renders each
surface from the same `StatusSurfaceSelections` snapshot.

4. **`chatwidget.rs`** sets `TerminalTitleStatusKind` at each state
transition (Working, Thinking, Undoing, WaitingForBackgroundTerminal)
and calls `refresh_terminal_title()` whenever relevant state changes.

5. **`app.rs`** handles the three setup events (confirm/preview/cancel),
persists config via `ConfigEditsBuilder`, and clears the managed title
on `Drop`.

## Non-goals

- **Restoring the previous terminal title on exit.** There is no
portable way to read the terminal's current title, so `Drop` clears the
managed title rather than restoring it.
- **Sharing code between `tui` and `tui_app_server`.** The
implementation is a parallel copy, matching the existing pattern for the
status-line feature. Extracting a shared crate is future work.

## Tradeoffs

- **Duplicate code across crates.** The three core files
(`terminal_title.rs`, `title_setup.rs`, `status_surfaces.rs`) are
byte-for-byte copies from the classic `tui`. This was chosen for
consistency with the existing status-line port and to avoid coupling the
two crates at the dependency level. Future changes must be applied in
both places.

- **`status_surfaces.rs` is large (~660 lines).** It absorbs logic that
previously lived inline in `chatwidget.rs` (status-line refresh, git
branch management, project root discovery) plus all new terminal-title
logic. This consolidation trades file size for a single place where both
surfaces are coordinated.

- **Spinner scheduling on every refresh.** The terminal title spinner
(when active) schedules a frame every 100ms. This is the same pattern
the status-indicator spinner already uses; the overhead is a timer
registration, not a redraw.

## Architecture

```
/title command
  -> SlashCommand::Title
  -> open_terminal_title_setup()
  -> TerminalTitleSetupView (MultiSelectPicker)
  -> on_change:  AppEvent::TerminalTitleSetupPreview  -> preview_terminal_title()
  -> on_confirm: AppEvent::TerminalTitleSetup         -> ConfigEditsBuilder + setup_terminal_title()
  -> on_cancel:  AppEvent::TerminalTitleSetupCancelled -> cancel_terminal_title_setup()

Runtime title refresh:
  state change (turn start, reasoning, undo, plan update, thread rename, ...)
  -> set terminal_title_status_kind
  -> refresh_terminal_title()
  -> status_surface_selections()  (parse configs, collect invalids)
  -> refresh_terminal_title_from_selections()
     -> terminal_title_value_for_item() for each configured item
     -> assemble title string with separators
     -> skip if identical to last_terminal_title (dedup OSC writes)
     -> set_terminal_title() (sanitize + OSC 0 write)
     -> schedule spinner frame if animating

Widget replacement:
  replace_chat_widget_with_app_server_thread()
  -> transfer last_terminal_title from old widget to new
  -> avoids redundant OSC clear+rewrite on session switch
```

## Observability

- Invalid terminal-title item IDs in config emit a one-per-session
warning via `on_warning()` (gated by
`terminal_title_invalid_items_warned` `AtomicBool`).
- OSC write failures are logged at `tracing::debug` level.
- Config persistence failures are logged at `tracing::error` and
surfaced to the user via `add_error_message()`.

## Tests

- `terminal_title.rs`: 4 unit tests covering sanitization (control
chars, bidi codepoints, truncation) and OSC output format.
- `title_setup.rs`: 3 tests covering setup view snapshot rendering,
parse order preservation, and invalid-ID rejection.
- `chatwidget/tests.rs`: Updated test helpers with new fields; existing
tests continue to pass.

---------

Co-authored-by: Eric Traut <etraut@openai.com>

codex-rs/tui_app_server/src/app_event.rs

@@ -28,6 +28,7 @@ use codex_utils_approval_presets::ApprovalPreset;
 
 use crate::bottom_pane::ApprovalRequest;
 use crate::bottom_pane::StatusLineItem;
+use crate::bottom_pane::TerminalTitleItem;
 use crate::history_cell::HistoryCell;
 
 use codex_core::config::types::ApprovalsReviewer;
@@ -547,6 +548,17 @@ pub(crate) enum AppEvent {
     /// Dismiss the status-line setup UI without changing config.
     StatusLineSetupCancelled,
 
+    /// Apply a user-confirmed terminal-title item ordering/selection.
+    TerminalTitleSetup {
+        items: Vec<TerminalTitleItem>,
+    },
+    /// Apply a temporary terminal-title preview while the setup UI is open.
+    TerminalTitleSetupPreview {
+        items: Vec<TerminalTitleItem>,
+    },
+    /// Dismiss the terminal-title setup UI without changing config.
+    TerminalTitleSetupCancelled,
+
     /// Apply a user-confirmed syntax theme selection.
     SyntaxThemeSelected {
         name: String,