feat: add session score display and refactor Jenkinsfile

Score tracks X wins, O wins, draws in-memory for current session.
Jenkinsfile rewritten as scripted pipeline with named execute functions
and per-branch strategy closures (mirrors BasePipeline pattern).

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

public/game.js

@@ -6,9 +6,13 @@
   ];
 
   let board, current, over;
+  const score = { X: 0, O: 0, draw: 0 };
   const cells = document.querySelectorAll('.cell');
   const status = document.getElementById('status');
   const resetBtn = document.getElementById('reset');
+  const scoreX = document.getElementById('score-x');
+  const scoreO = document.getElementById('score-o');
+  const scoreDraw = document.getElementById('score-draw');
 
   function init() {
     board = Array(9).fill(null);
@@ -43,8 +47,12 @@
     if (result) {
       over = true;
       if (result.draw) {
+        score.draw++;
+        scoreDraw.textContent = score.draw;
         status.textContent = "It's a draw!";
       } else {
+        score[result.winner]++;
+        (result.winner === 'X' ? scoreX : scoreO).textContent = score[result.winner];
         result.line.forEach(i => cells[i].classList.add('winner'));
         status.textContent = `Player ${result.winner} wins!`;
       }