Fix markdown streaming duplication by splitting newlines first

- Added string-width library for proper terminal column width calculation
- Fixed wrapLine() to split by newlines before wrapping (like Text component)
- Fixed Loader interval leak by stopping before container removal
- Changed loader message from 'Loading...' to 'Working...'

packages/tui/src/index.ts

@@ -17,4 +17,6 @@ export { Spacer } from "./components/spacer.js";
 export { Text } from "./components/text.js";
 // Terminal interface and implementations
 export { ProcessTerminal, type Terminal } from "./terminal.js";
-export { Component, Container, TUI } from "./tui.js";
+export { type Component, Container, TUI } from "./tui.js";
+// Utilities
+export { visibleWidth } from "./utils.js";