Prework Milestone 3: Adding player movement

**Problem:**
I want to add the ability to move my avatar using the arrow keys.

**Implementation Suggestions:**
This is blocked first by #8 and #9 so we should handle those first

Holding down the arrow keys should move the player continuously, and don’t rate limit the move commands.

**Testing Criteria:**
Open index.html in Chrome and confirm that we can send one move command per key down event.

Resolve or inspect issues #8 and #9 first, since this work is explicitly blocked by them. Then open index.html in Chrome and trace the existing movement or command handling. Done means arrow-key input sends one move command per key-down event and holding a key moves the avatar continuously without rate limiting.

Written by the indexing model from the issue text.