Add goal TUI UX (5 / 5) (#18077)

Adds the TUI user experience for goals on top of the core runtime from
PR 4.

## Why

Users need a direct TUI control surface for long-running goals. The UI
should make the current goal visible, support common goal actions
without waiting for a model turn, and avoid confusing end-of-turn
notifications while an active goal is immediately continuing.

## What changed

- Added `/goal` summary rendering for the current goal, including
active, paused, budget-limited, and complete states.
- Added `/goal <objective>` creation/replacement through the app-server
goal API rather than a model prompt.
- Added `/goal clear`, `/goal pause`, and `/goal unpause` command
variants.
- Added a confirmation menu when the user enters a new goal while
another goal already exists.
- Updated `/goal` help and summary tip text so it reflects the supported
command variants without advertising slash-command token budgets.
- Added footer/statusline goal indicators, including elapsed time and
token budget display when a budget exists from API/tool-created goals.
- Consumes goal updated/cleared notifications so the TUI stays in sync
with external app-server changes.
- Suppresses end-of-turn desktop notifications only when a goal is still
active and follow-up work is expected.
- Preserves slash-command history behavior and avoids leaking queued
`/goal` state into unrelated submissions.

## Verification

- Added TUI unit and snapshot coverage for goal command availability,
summary rendering, control commands, replacement menu behavior,
status/footer display, notification handling, and command history.

codex-rs/tui/src/app/event_dispatch.rs

@@ -471,6 +471,24 @@ impl App {
             AppEvent::RefreshRateLimits { origin } => {
                 self.refresh_rate_limits(app_server, origin);
             }
+            AppEvent::OpenThreadGoalMenu { thread_id } => {
+                self.open_thread_goal_menu(app_server, thread_id).await;
+            }
+            AppEvent::SetThreadGoalObjective {
+                thread_id,
+                objective,
+                mode,
+            } => {
+                self.set_thread_goal_objective(app_server, thread_id, objective, mode)
+                    .await;
+            }
+            AppEvent::SetThreadGoalStatus { thread_id, status } => {
+                self.set_thread_goal_status(app_server, thread_id, status)
+                    .await;
+            }
+            AppEvent::ClearThreadGoal { thread_id } => {
+                self.clear_thread_goal(app_server, thread_id).await;
+            }
             AppEvent::SendAddCreditsNudgeEmail { credit_type } => {
                 if self
                     .chat_widget