Refactor TUI into proper components

- Create UserMessageComponent - handles user messages with spacing
- Create AssistantMessageComponent - handles complete assistant messages
- Create ThinkingSelectorComponent - wraps selector with borders
- Add setSelectedIndex to SelectList for preselecting current level
- Simplify tui-renderer by using dedicated components
- Much cleaner architecture - each message type is now a component

packages/coding-agent/src/tui/user-message.ts

@@ -0,0 +1,23 @@
+import { Container, Markdown, Spacer } from "@mariozechner/pi-tui";
+
+/**
+ * Component that renders a user message
+ */
+export class UserMessageComponent extends Container {
+	private spacer: Spacer | null = null;
+	private markdown: Markdown;
+
+	constructor(text: string, isFirst: boolean) {
+		super();
+
+		// Add spacer before user message (except first one)
+		if (!isFirst) {
+			this.spacer = new Spacer(1);
+			this.addChild(this.spacer);
+		}
+
+		// User messages with dark gray background
+		this.markdown = new Markdown(text, undefined, undefined, { r: 52, g: 53, b: 65 });
+		this.addChild(this.markdown);
+	}
+}