Keep slash command popup columns stable while scrolling (#19511)

## Why

Fixes #19499.

The slash-command popup recalculated the command-name column from only
the rows visible in the current viewport. That made the description
column shift horizontally while scrolling through `/` commands whenever
longer command names entered or left the visible window.

## What Changed

`codex-rs/tui/src/bottom_pane/command_popup.rs` now uses the shared
selection-popup `AutoAllRows` column-width mode for both height
measurement and rendering. This keeps the command description column
based on the full filtered slash-command list instead of the current
viewport.

## Verification

- `cargo test -p codex-tui bottom_pane::command_popup`

codex-rs/tui/src/bottom_pane/command_popup.rs

@@ -4,8 +4,11 @@ use ratatui::widgets::WidgetRef;
 
 use super::popup_consts::MAX_POPUP_ROWS;
 use super::scroll_state::ScrollState;
+use super::selection_popup_common::ColumnWidthConfig;
+use super::selection_popup_common::ColumnWidthMode;
 use super::selection_popup_common::GenericDisplayRow;
-use super::selection_popup_common::render_rows;
+use super::selection_popup_common::measure_rows_height_with_col_width_mode;
+use super::selection_popup_common::render_rows_with_col_width_mode;
 use super::slash_commands;
 use crate::render::Insets;
 use crate::render::RectExt;
@@ -15,6 +18,10 @@ use crate::slash_command::SlashCommand;
 // `quit` is an alias of `exit`, so we skip `quit` here.
 // `approvals` is an alias of `permissions`.
 const ALIAS_COMMANDS: &[SlashCommand] = &[SlashCommand::Quit, SlashCommand::Approvals];
+const COMMAND_COLUMN_WIDTH: ColumnWidthConfig = ColumnWidthConfig::new(
+    ColumnWidthMode::AutoAllRows,
+    /*name_column_width*/ None,
+);
 
 /// A selectable item in the popup.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
@@ -109,10 +116,15 @@ impl CommandPopup {
     /// Determine the preferred height of the popup for a given width.
     /// Accounts for wrapped descriptions so that long tooltips don't overflow.
     pub(crate) fn calculate_required_height(&self, width: u16) -> u16 {
-        use super::selection_popup_common::measure_rows_height;
         let rows = self.rows_from_matches(self.filtered());
 
-        measure_rows_height(&rows, &self.state, MAX_POPUP_ROWS, width)
+        measure_rows_height_with_col_width_mode(
+            &rows,
+            &self.state,
+            MAX_POPUP_ROWS,
+            width,
+            COMMAND_COLUMN_WIDTH,
+        )
     }
 
     /// Compute exact/prefix matches over built-in commands and user prompts,
@@ -223,7 +235,7 @@ impl CommandPopup {
 impl WidgetRef for CommandPopup {
     fn render_ref(&self, area: Rect, buf: &mut Buffer) {
         let rows = self.rows_from_matches(self.filtered());
-        render_rows(
+        render_rows_with_col_width_mode(
             area.inset(Insets::tlbr(
                 /*top*/ 0, /*left*/ 2, /*bottom*/ 0, /*right*/ 0,
             )),
@@ -232,6 +244,7 @@ impl WidgetRef for CommandPopup {
             &self.state,
             MAX_POPUP_ROWS,
             "no matches",
+            COMMAND_COLUMN_WIDTH,
         );
     }
 }