feat: implement falling letters spawning from top

- Letters spawn at random horizontal positions every 1 second
- Letters fall at 100px/second from top to bottom
- Random A-Z letters rendered in white monospace font
- Fix game loop to start properly when startGame called
- Remove letters that exit bottom of screen

src/useGame/useGame.ts

@@ -1,4 +1,4 @@
-import { useState, useEffect } from "react";
+import { useState, useEffect, useCallback } from "react";
 import type { GameManager, GameOptions, KeyLogEntry } from "../types";
 import { useBoard } from "../useBoard";
 import { useCursor } from "../useCursor";
@@ -13,18 +13,24 @@ export function useGame(
 
   const boardManager = useBoard();
   const cursorManager = useCursor();
-  const gameStatusManager = useGameStatus();
-  const scoreManager = useScore(gameStatusManager);
 
   // Wrap renderBoard to include player position
-  const renderBoardWrapped = () => {
-    boardManager.renderBoard(cursorManager.position());
-  };
+  const renderBoardWrapped = useCallback((letters: any = []) => {
+    boardManager.renderBoard(cursorManager.position(), letters);
+  }, [boardManager, cursorManager]);
+
+  // Game loop tick handler
+  const handleGameLoopTick = useCallback((_deltaTime: number, letters: any) => {
+    renderBoardWrapped(letters);
+  }, [renderBoardWrapped]);
+
+  const gameStatusManager = useGameStatus(handleGameLoopTick);
+  const scoreManager = useScore(gameStatusManager);
 
   // Initial render on mount
   useEffect(() => {
     renderBoardWrapped();
-  }, []);
+  }, [renderBoardWrapped]);
 
   const gameManager: GameManager = {
     containerRef: boardManager.containerRef,