Separate directory and repository scopes in the TUI (#56308)

## Why

The `Cwd` session filter included sessions from linked worktrees, leaving no way to restrict the picker to the current directory. Project grouping also combined tasks across linked worktrees.

## What changed

- Keep `Cwd` filtering and directory-scoped `resume --last` and `fork --last` lookups limited to the current directory.
- Add an explicit `Repo` picker filter when multiple local worktrees are available, including sessions from corresponding directories across linked worktrees. Cycle between `Cwd`, `Repo`, and `All` in either direction.
- Add `Directory` grouping to the agent command center alongside `Project`, `Status`, and `Model`. Keep this choice in memory without writing a configuration value older clients cannot read.

## Testing

Extend coverage for directory and repository filtering, pagination scope, linked-worktree grouping, directory aliases, grouping persistence, and adjacent selection after task removal. Update picker and command center snapshots.

GitOrigin-RevId: 59603c9c5136db43124102b3277d1d1dab36bb87

codex-rs/tui/src/keymap_setup/actions.rs

@@ -278,7 +278,7 @@ define_keymap_actions! {
         archive => "Archive the selected task and its child agents.",
         delete => "Permanently delete the selected task and its child agents.",
         hide => "Hide the selected task until explicitly resumed.",
-        toggle_grouping => "Cycle task grouping by project, status, or model.",
+        toggle_grouping => "Cycle task grouping by project, directory, status, or model.",
     }
     approval "Approval" {
         open_fullscreen => "Open approval details fullscreen.",