feat(coding-agent): add ctx.ui.setEditorComponent() extension API

- Add setEditorComponent() to ctx.ui for custom editor components
- Add CustomEditor base class for extensions (handles app keybindings)
- Add keybindings parameter to ctx.ui.custom() factory (breaking change)
- Add modal-editor.ts example (vim-like modes)
- Add rainbow-editor.ts example (animated text highlighting)
- Update docs: extensions.md, tui.md Pattern 7
- Clean up terminal on TUI render errors

packages/coding-agent/src/modes/interactive/components/custom-editor.ts

@@ -6,7 +6,7 @@ import type { AppAction, KeybindingsManager } from "../../../core/keybindings.js
  */
 export class CustomEditor extends Editor {
 	private keybindings: KeybindingsManager;
-	private actionHandlers: Map<AppAction, () => void> = new Map();
+	public actionHandlers: Map<AppAction, () => void> = new Map();
 
 	// Special handlers that can be dynamically replaced
 	public onEscape?: () => void;