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/tui/src/components/select-list.ts

@@ -1,4 +1,4 @@
-import { isArrowDown, isArrowUp, isCtrlC, isEnter, isEscape } from "../keys.js";
+import { matchesKey } from "../keys.js";
 import type { Component } from "../tui.js";
 import { truncateToWidth } from "../utils.js";
 
@@ -146,24 +146,24 @@ export class SelectList implements Component {
 
 	handleInput(keyData: string): void {
 		// Up arrow - wrap to bottom when at top
-		if (isArrowUp(keyData)) {
+		if (matchesKey(keyData, "up")) {
 			this.selectedIndex = this.selectedIndex === 0 ? this.filteredItems.length - 1 : this.selectedIndex - 1;
 			this.notifySelectionChange();
 		}
 		// Down arrow - wrap to top when at bottom
-		else if (isArrowDown(keyData)) {
+		else if (matchesKey(keyData, "down")) {
 			this.selectedIndex = this.selectedIndex === this.filteredItems.length - 1 ? 0 : this.selectedIndex + 1;
 			this.notifySelectionChange();
 		}
 		// Enter
-		else if (isEnter(keyData)) {
+		else if (matchesKey(keyData, "enter")) {
 			const selectedItem = this.filteredItems[this.selectedIndex];
 			if (selectedItem && this.onSelect) {
 				this.onSelect(selectedItem);
 			}
 		}
 		// Escape or Ctrl+C
-		else if (isEscape(keyData) || isCtrlC(keyData)) {
+		else if (matchesKey(keyData, "escape") || matchesKey(keyData, "ctrl+c")) {
 			if (this.onCancel) {
 				this.onCancel();
 			}