Fix garbage elimination bug and align board with header

- Change y-- instead of y++ when pushing piece up on garbage
- Add y < 0 check to properly detect piece pushed off top
- Remove margin-top from battle grid to align with header

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

public/css/style.css

@@ -197,7 +197,6 @@ button:active {
   display: flex;
   justify-content: center;
   align-items: center;
-  margin-top: 20px;
 }
 
 /* Main player board - centered and large */

server/index.js

@@ -396,11 +396,11 @@ function addGarbageToPlayer(player) {
   garbageRow[Math.floor(Math.random() * BOARD_WIDTH)] = 0;
   player.board.push(garbageRow);
 
-  // Push current piece up by 1 row if it exists
+  // Push current piece up by 1 row if it exists (y decreases when moving up)
   if (player.currentPiece) {
-    player.currentPiece.y++;
-    // Eliminate if the piece is pushed above the board
-    if (!isValidPosition(player.currentPiece, player.currentPiece.x, player.currentPiece.y, player.board)) {
+    player.currentPiece.y--;
+    // Eliminate if the piece is pushed above the board or collides
+    if (player.currentPiece.y < 0 || !isValidPosition(player.currentPiece, player.currentPiece.x, player.currentPiece.y, player.board)) {
       player.eliminated = true;
     }
   }