feat: add configurable keybinds for slash commands

Summary

Add a keybinds settings field that maps keyboard shortcuts directly to slash command actions, so users can trigger commands like /exit, /new, /skills without typing /. Also adds a /keybind slash command for runtime management (add/remove/list).

Motivation

Currently, all slash commands require typing /command + Enter. For frequent operations (exiting, starting a new session, opening the skills list), a keyboard shortcut is faster and more ergonomic. This feature lets users configure their own shortcuts and manage them at runtime without editing JSON by hand.

Design

Configuration

New top-level field settings.keybinds:

{
  "keybinds": {
    "ctrl+e": "exit",
    "ctrl+n": "new",
    "ctrl+s": "skills",
    "ctrl+m": "model"
  }
}

• Shortcut format: ctrl+key, ctrl+shift+key, or meta+key
• Action value: any slash command name or skill name
• Project settings override user settings per shortcut key
• Custom keybinds only fire when no dropdown/menu is open (avoids conflicts)

Runtime management

The /keybind slash command supports three subcommands:

/keybind add ctrl+e exit
/keybind remove ctrl+e
/keybind list

Changes are persisted to settings.json immediately and take effect without restarting.

Architecture

The feature follows the same pattern as statusline and enabledSkills:

• Core layer (packages/core/src/settings.ts): KeybindMap type, normalizeKeybinds(), mergeKeybinds(), integration into resolveSettingsSources()
• Parser (packages/cli/src/ui/core/keybinds.ts): matchKeybind() converts shortcut strings (e.g. "ctrl+shift+g") into exact-modifier predicates against InputKey; buildKeybindMatchers() pre-compiles a map for fast per-keystroke lookup
• Input integration (PromptInput.tsx): keybinds are checked before hardcoded shortcuts, resolving the action name to a SlashCommandItem and dispatching via handleSlashSelection()
• Slash command (slash-commands.ts): new "keybind" kind with subcommand parsing in handleKeybindCommand(), reading/writing settings with project-over-user fallback

Files Changed

Verification

npm run check     — typecheck 0 errors, lint 0 errors (1 pre-existing warning), format clean
npm test          — 269 tests, 0 fail
npm run build     — successful