[FEATURE] Support CSI u keyboard protocol for Ctrl+[ (ESC equivalent)

Description

Claude Code does not properly handle Ctrl+[ as ESC when using modern terminal emulators with CSI u keyboard protocol enabled (e.g., Ghostty, kitty with keyboard_protocol=kitty enabled).

Environment

• Claude Code version: 2.1.6
• Terminal: Ghostty (CSI u protocol enabled by default)
• OS: macOS 15.1

Current Behavior

When CSI u keyboard protocol is enabled:

• Pressing Ctrl+[ in Claude Code's confirmation dialogs (e.g., "Do you want to proceed? Esc to cancel") does nothing
• The key is encoded as CSI 91;5u format instead of being recognized as ESC
• In fzf launched from Claude Code, pressing Ctrl+[ displays 91;5u literally

Expected Behavior

Ctrl+[ should function as ESC in Claude Code's TUI, just like in other CSI u-aware applications:

• ✅ Vim/Neovim: Ctrl+[ correctly functions as ESC
• ✅ Fish shell: CSI u protocol works perfectly for advanced key bindings
• ❌ Claude Code: Ctrl+[ is not recognized as ESC

Why This Matters

1. Modern terminal standard: CSI u is becoming the standard keyboard protocol for modern terminal emulators
2. Ergonomics: Ctrl+[ is more ergonomic than reaching for ESC key (especially on keyboards without physical ESC)
3. Consistency: Other modern CLI tools (vim, neovim, fish) already support it

Workaround

Currently, users must use the physical ESC key instead of Ctrl+[, which defeats the purpose of using modern keyboard protocols.

References

• CSI u keyboard protocol: https://sw.kovidgoyal.net/kitty/keyboard-protocol/
• Ghostty terminal (uses CSI u by default): https://ghostty.org/