Remove hard-coded black color from animated-letters example

The example was setting color: "black" on letter spans, which made them
invisible on dark backgrounds. Now letters inherit the default text color
which adapts to the current color scheme (light/dark mode).

The animation still works - letters appear green, turn red when leaving,
and are visible (not black) during their steady state.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: claude

examples/animated-letters.js

@@ -64,7 +64,7 @@ function* Letter({letter, index}) {
 			});
 		});
 
-		yield <span style={{...style, color: "black"}}>{letter}</span>;
+		yield <span style={style}>{letter}</span>;
 	}
 }