feat: implement terminal control functions

[mjm918]

Summary

Add terminal control functions to naml runtime for building TUI applications and games.

Proposed API

// Clear the terminal screen
fn clear_screen();

// Move cursor to position (0-indexed)
fn set_cursor(x: int, y: int);

// Hide/show cursor
fn hide_cursor();
fn show_cursor();

// Get terminal dimensions
fn terminal_width() -> int;
fn terminal_height() -> int;

Use Cases

• Terminal games (snake, tetris, roguelikes)
• TUI applications
• Progress bars and animations
• Dashboard displays

Implementation Notes

• Use ANSI escape sequences for cross-platform compatibility
• Platform considerations:
  • Native: Write ANSI sequences to stdout, use ioctl for dimensions
  • Server WASM: Same ANSI sequences via WASI stdout
  • Browser: Not applicable

ANSI Reference

• Clear screen: \x1b[2J
• Move cursor: \x1b[{row};{col}H
• Hide cursor: \x1b[?25l
• Show cursor: \x1b[?25h

Acceptance Criteria

• clear_screen() clears terminal content
• set_cursor(x, y) positions cursor correctly
• hide_cursor() / show_cursor() work
• terminal_width() / terminal_height() return correct dimensions
• Works on native platform with standard terminals

[mjm918]

Implemented in commit f229b51. All 6 functions available via use std::io::*;