fix: allow legacy terminal keyboard reporting

[mvanhorn]

Checks

• I am happy for maintainers to push small adjustments to this PR, to speed up the review cycle

Fixes #2559

[greptile-apps]

Push failure skips terminal cleanup

When writing PushKeyboardEnhancementFlags fails, Stdout::new returns after raw mode, alternate-screen, mouse, and bracketed-paste setup but before Stdout reaches its caller, so its cleanup Drop never runs and the shell remains in a corrupted terminal state.

Knowledge Base Used: CLI entrypoint (atuin binary)

[greptile-apps]

Greptile Summary

Adds a keyboard_enhancement setting, conditionally enables terminal keyboard-enhancement flags during interactive search, and documents legacy key reporting.

Confidence Score: 3/5

The terminal cleanup failure on keyboard-enhancement setup needs to be fixed before merging.

The new fallible keyboard-enhancement push occurs after terminal modes are enabled, and returning from that operation bypasses the cleanup guard that would restore the shell.

Files Needing Attention: crates/atuin/src/command/client/search/interactive.rs

Important Files Changed

Filename	Overview
crates/atuin-client/src/settings.rs	Adds the boolean setting with a default, override coverage, and validation tests.
crates/atuin/src/command/client/search/interactive.rs	Conditionally pushes keyboard-enhancement flags, but a failed push bypasses cleanup of terminal modes enabled earlier in construction.
docs/docs/configuration/advanced-key-binding.md	Documents legacy-mode compatibility and its advanced-keybinding limitations.

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