feat(tui, coding-agent): add configurable code block indent setting (#855)

Add markdown.codeBlockIndent setting to customize indentation prefix for
rendered code blocks. Default remains 2 spaces for visual clarity, but
setting to empty string removes indentation for easier copy/paste of
code snippets to scripts, editors, or other tools.

Changes:
- tui: add optional codeBlockIndent to MarkdownTheme interface
- coding-agent: add MarkdownSettings with codeBlockIndent property
- coding-agent: compose theme with settings at call sites (no global state)
- coding-agent: update message components to accept optional MarkdownTheme

Co-authored-by: Mario Zechner <badlogicgames@gmail.com>

packages/coding-agent/src/modes/interactive/components/user-message.ts

@@ -1,15 +1,15 @@
-import { Container, Markdown, Spacer } from "@mariozechner/pi-tui";
+import { Container, Markdown, type MarkdownTheme, Spacer } from "@mariozechner/pi-tui";
 import { getMarkdownTheme, theme } from "../theme/theme.js";
 
 /**
  * Component that renders a user message
  */
 export class UserMessageComponent extends Container {
-	constructor(text: string) {
+	constructor(text: string, markdownTheme: MarkdownTheme = getMarkdownTheme()) {
 		super();
 		this.addChild(new Spacer(1));
 		this.addChild(
-			new Markdown(text, 1, 1, getMarkdownTheme(), {
+			new Markdown(text, 1, 1, markdownTheme, {
 				bgColor: (text: string) => theme.bg("userMessageBg", text),
 				color: (text: string) => theme.fg("userMessageText", text),
 			}),