✨ Add countdown timer to typing game

[bhattk64]

Summary

This PR adds a 30-second countdown timer to the typing game in the 4-typing-game lesson.

Features:

• Timer starts when the game begins
• Timer stops when the user finishes or time runs out
• Input disables after timeout
• Success or timeout messages displayed

This helps simulate time pressure and adds replayability to the game.

[bhattk64]

@microsoft-github-policy-service agree

[leestott]

@bhattk64 please resolve branch conflicts