feat(tui): standardize picker navigation keys (#22347)

## Why

Picker-style UI in the TUI has accumulated a mix of hardcoded navigation
keys. Some lists supported page movement, some did not; some accepted
Vim-like keys, while others only accepted arrows; and tabbed or
horizontally adjustable pickers had no shared keymap action for
left/right movement.

This PR makes picker/list navigation consistent and configurable so
users can rely on the same defaults across the TUI.

## What Changed

- Adds shared list keymap actions for:
  - vertical movement: `move_up`, `move_down`
  - horizontal movement: `move_left`, `move_right`
  - paging and jumps: `page_up`, `page_down`, `jump_top`, `jump_bottom`
- Adds defaults:
- Up/down: arrows, `Ctrl+P/N`, `Ctrl+K/J`, and plain `k/j` where text
input is not active
  - Page up/down: `PageUp/PageDown` and `Ctrl+B/F`
  - First/last: `Home/End`
  - Left/right: `Left/Right` and `Ctrl+H/L`
- Wires the shared list keymap through picker and list surfaces
including session resume, multi-select, tabbed selection lists,
settings-style lists, app-link selection, MCP elicitation,
request-user-input, and the OSS selection wizard.
- Keeps search behavior intact by reserving printable characters for
query text in searchable pickers.
- Updates keymap setup actions, config schema, snapshots, and focused
coverage for the new list actions.

## How to Test

1. Start Codex from this branch and open the session picker, for example
with an existing session history.
2. In the session list, verify that `Ctrl+J/K` moves the selection
down/up.
3. Verify that `Ctrl+F/B` pages down/up and `Home/End` jumps to the
first/last visible session.
4. Type printable search text such as `j` or `k` and confirm it updates
the query instead of navigating.
5. Focus a picker control that changes values horizontally, such as a
session picker toolbar control, and verify `Ctrl+H/L` changes the
focused value like left/right arrows.

Targeted tests run:

- `cargo test -p codex-tui keymap::tests::`
- `cargo test -p codex-tui keymap_setup::tests::`
- `cargo test -p codex-tui horizontal_list_keys`
- `cargo test -p codex-tui page_and_jump_navigation_use_list_keymap`
- `cargo test -p codex-tui ctrl_h_l_move_provider_selection`
- `cargo test -p codex-tui scroll_state::tests`
- `cargo test -p codex-tui
switching_tabs_changes_visible_items_and_clears_search`
- `cargo test -p codex-tui toggle_sort_key_reloads_with_new_sort`

Also ran `just write-config-schema`, `just fmt`, `just fix -p
codex-tui`, `just argument-comment-lint`, and `git diff --check`.

Note: `cargo test -p codex-tui` was attempted and still aborts in the
pre-existing
`tests::fork_last_filters_latest_session_by_cwd_unless_show_all` stack
overflow, which is unrelated to this branch.

codex-rs/config/src/tui_keymap.rs

@@ -306,6 +306,18 @@ pub struct TuiListKeymap {
     pub move_up: Option<KeybindingsSpec>,
     /// Move list selection down.
     pub move_down: Option<KeybindingsSpec>,
+    /// Move horizontally left in list pickers that support horizontal actions.
+    pub move_left: Option<KeybindingsSpec>,
+    /// Move horizontally right in list pickers that support horizontal actions.
+    pub move_right: Option<KeybindingsSpec>,
+    /// Move list selection up by one page.
+    pub page_up: Option<KeybindingsSpec>,
+    /// Move list selection down by one page.
+    pub page_down: Option<KeybindingsSpec>,
+    /// Jump to the first list item.
+    pub jump_top: Option<KeybindingsSpec>,
+    /// Jump to the last list item.
+    pub jump_bottom: Option<KeybindingsSpec>,
     /// Accept current selection.
     pub accept: Option<KeybindingsSpec>,
     /// Cancel and close selection view.