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/examples/extensions/qna.ts

@@ -71,7 +71,7 @@ export default function (pi: ExtensionAPI) {
 			}
 
 			// Run extraction with loader UI
-			const result = await ctx.ui.custom<string | null>((tui, theme, done) => {
+			const result = await ctx.ui.custom<string | null>((tui, theme, _kb, done) => {
 				const loader = new BorderedLoader(tui, theme, `Extracting questions using ${ctx.model!.id}...`);
 				loader.onAbort = () => done(null);