feat: configurable keybindings for all editor and app actions

All keybindings configurable via ~/.pi/agent/keybindings.json

Editor actions:
- cursorUp, cursorDown, cursorLeft, cursorRight
- cursorWordLeft, cursorWordRight, cursorLineStart, cursorLineEnd
- deleteCharBackward, deleteCharForward, deleteWordBackward
- deleteToLineStart, deleteToLineEnd
- newLine, submit, tab
- selectUp, selectDown, selectConfirm, selectCancel

App actions:
- interrupt, clear, exit, suspend
- cycleThinkingLevel, cycleModelForward, cycleModelBackward
- selectModel, expandTools, toggleThinking, externalEditor

Also adds support for numpad Enter key (Kitty protocol codepoint 57414
and SS3 M sequence)

Example emacs-style keybindings.json:
{
  "cursorUp": ["up", "ctrl+p"],
  "cursorDown": ["down", "ctrl+n"],
  "cursorLeft": ["left", "ctrl+b"],
  "cursorRight": ["right", "ctrl+f"],
  "deleteCharForward": ["delete", "ctrl+d"],
  "cycleModelForward": "ctrl+o"
}

packages/coding-agent/examples/hooks/todo/index.ts

@@ -6,7 +6,7 @@
  */
 
 import type { HookAPI, Theme } from "@mariozechner/pi-coding-agent";
-import { isCtrlC, isEscape, truncateToWidth } from "@mariozechner/pi-tui";
+import { matchesKey, truncateToWidth } from "@mariozechner/pi-tui";
 
 interface Todo {
 	id: number;
@@ -35,7 +35,7 @@ class TodoListComponent {
 	}
 
 	handleInput(data: string): void {
-		if (isEscape(data) || isCtrlC(data)) {
+		if (matchesKey(data, "escape") || matchesKey(data, "ctrl+c")) {
 			this.onClose();
 		}
 	}