Add ctx.ui.theme getter for styling status text with theme colors

- Add theme property to HookUIContext interface
- Implement in interactive, RPC, and no-op contexts
- Add status-line.ts example hook
- Document styling with theme colors in hooks.md

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -375,6 +375,9 @@ export class InteractiveMode {
 			custom: (factory) => this.showHookCustom(factory),
 			setEditorText: (text) => this.editor.setText(text),
 			getEditorText: () => this.editor.getText(),
+			get theme() {
+				return theme;
+			},
 		};
 		this.setToolUIContext(uiContext, true);