feat(tui2): copy tui crate and normalize snapshots (#7833)

Introduce a full codex-tui source snapshot under the new codex-tui2
crate so viewport work can be replayed in isolation.

This change copies the entire codex-rs/tui/src tree into
codex-rs/tui2/src in one atomic step, rather than piecemeal, to keep
future diffs vs the original viewport bookmark easy to reason about.

The goal is for codex-tui2 to render identically to the existing TUI
behind the `features.tui2` flag while we gradually port the
viewport/history commits from the joshka/viewport bookmark onto this
forked tree.

While on this baseline change, we also ran the codex-tui2 snapshot test
suite and accepted all insta snapshots for the new crate, so the
snapshot files now use the codex-tui2 naming scheme and encode the
unmodified legacy TUI behavior. This keeps later viewport commits
focused on intentional behavior changes (and their snapshots) rather
than on mechanical snapshot renames.

codex-rs/cli/src/main.rs

@@ -663,7 +663,8 @@ async fn run_interactive_tui(
     codex_linux_sandbox_exe: Option<PathBuf>,
 ) -> std::io::Result<AppExitInfo> {
     if is_tui2_enabled(&interactive).await? {
-        tui2::run_main(interactive, codex_linux_sandbox_exe).await
+        let result = tui2::run_main(interactive.into(), codex_linux_sandbox_exe).await?;
+        Ok(result.into())
     } else {
         codex_tui::run_main(interactive, codex_linux_sandbox_exe).await
     }