Right-align grid cell index, count stays left

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

public/app.mjs

@@ -1308,6 +1308,7 @@ function render_grid_viewer() {
 
 		const index_span = document.createElement('span');
 		index_span.textContent = `R${row + 1}C${col + 1}`;
+		index_span.style.marginLeft = 'auto';
 		label_el.appendChild(index_span);
 
 		cell.addEventListener('click', (e) => open_cell_inventory(grid, row, col, e));