Mobile Support: Add Virtual Keyboard via Hidden Input

[vivinarya]

Problem: No support for touch/mobile users due to lack of keyboard.

Task:

• Add a hidden input field to index.html.
• When the canvas is touched, focus the input (shows mobile keyboard).
• Handle user input via the field and pass it to game logic in script.js.

Acceptance Criteria:

• Virtual keyboard appears on canvas tap for mobile users.
• All input is processed correctly regardless of device.
• Changes only in index.html and script.js.