This is a follow-up to https://github.com/openai/codex/pull/15922. That
previous PR deleted the old `tui` directory and left the new
`tui_app_server` directory in place. This PR renames `tui_app_server` to
`tui` and fixes up all references.
This is the part 1 of 2 PRs that will delete the `tui` /
`tui_app_server` split. This part simply deletes the existing `tui`
directory and marks the `tui_app_server` feature flag as removed. I left
the `tui_app_server` feature flag in place for now so its presence
doesn't result in an error. It is simply ignored.
Part 2 will rename the `tui_app_server` directory `tui`. I did this as
two parts to reduce visible code churn.
This PR adds a new `tui.notifications_method` config option that accepts
values of "auto", "osc9" and "bel". It defaults to "auto", which
attempts to auto-detect whether the terminal supports OSC 9 escape
sequences and falls back to BEL if not.
The PR also removes the inconsistent handling of notifications on
Windows when WSL was used.
