Remove legacy app-server notification handling from tui_app_server

[etraut-openai]

As part of moving the TUI onto the app server, we added some temporary handling of some legacy events. We've confirmed that these do not need to be supported, so this PR removes this support from the tui_app_server, allowing for additional simplifications in follow-on PRs. These events are needed only for very old rollouts. None of the other app server clients (IDE extension or app) support these either.

Summary

• stop translating legacy codex/event/* notifications inside tui_app_server
• remove the TUI-side legacy warning and rollback buffering/replay paths that were only fed by those notifications
• keep the lower-level app-server and app-server-client legacy event plumbing intact so PR Refactor codex exec to use typed app-server APIs #15106 can rebase on top and handle the remaining exec/lower-layer migration separately

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 05b63be19f

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".