fix(coding-agent): fix IME candidate window positioning in menu selectors

Components with search inputs now implement Focusable interface and
propagate focus state to their child Input components. This allows
the hardware cursor to be positioned correctly for IME candidate
window placement.

Affected components:
- ModelSelectorComponent
- ScopedModelsSelectorComponent
- SessionSelectorComponent (and SessionList)
- ExtensionInputComponent
- LoginDialogComponent
- TreeSelectorComponent (and LabelInput)

fixes #827

packages/coding-agent/src/modes/interactive/components/extension-input.ts

@@ -2,7 +2,7 @@
  * Simple text input component for extensions.
  */
 
-import { Container, getEditorKeybindings, Input, Spacer, Text, type TUI } from "@mariozechner/pi-tui";
+import { Container, type Focusable, getEditorKeybindings, Input, Spacer, Text, type TUI } from "@mariozechner/pi-tui";
 import { theme } from "../theme/theme.js";
 import { CountdownTimer } from "./countdown-timer.js";
 import { DynamicBorder } from "./dynamic-border.js";
@@ -13,7 +13,7 @@ export interface ExtensionInputOptions {
 	timeout?: number;
 }
 
-export class ExtensionInputComponent extends Container {
+export class ExtensionInputComponent extends Container implements Focusable {
 	private input: Input;
 	private onSubmitCallback: (value: string) => void;
 	private onCancelCallback: () => void;
@@ -21,6 +21,16 @@ export class ExtensionInputComponent extends Container {
 	private baseTitle: string;
 	private countdown: CountdownTimer | undefined;
 
+	// Focusable implementation - propagate to input for IME cursor positioning
+	private _focused = false;
+	get focused(): boolean {
+		return this._focused;
+	}
+	set focused(value: boolean) {
+		this._focused = value;
+		this.input.focused = value;
+	}
+
 	constructor(
 		title: string,
 		_placeholder: string | undefined,