feat(02-01): extend GameConfig, GameState, and Input for two-player support

- Add WIN_SCORE, AI_EASY, AI_MEDIUM, AI_HARD to GameConfig
- Add paddle2, score1, score2, mode, difficulty, gameState, winner to GameState
- Replace anonymous Input handlers with named refs + cleanup() method
- Add Input.getVerticalInput2() for ArrowUp/ArrowDown keys
- Position paddle2 on right side in Physics.init()
- Update Physics.onResize() to call init() for full repositioning

index.html

@@ -16,7 +16,13 @@
     const GameConfig = {
       initialBallSpeed: 220,    // px/s — starting speed per serve
       speedIncrement: 18,       // px/s added per paddle hit
-      paddleSpeed: 400          // px/s — Player 1 paddle movement
+      paddleSpeed: 400,         // px/s — Player 1 paddle movement
+
+      WIN_SCORE: 7,
+
+      AI_EASY:   { speed: 200, reactionDelay: 0.3,  errorMargin: 20 },
+      AI_MEDIUM: { speed: 320, reactionDelay: 0.1,  errorMargin: 5  },
+      AI_HARD:   { speed: 400, reactionDelay: 0.05, errorMargin: 2  }
     };
 
     const Renderer = {
@@ -99,28 +105,50 @@
         vx: 0, vy: 0,         // Set on Physics.init()
         speed: 0,             // Current scalar speed
         color: '#fff'
-      }
+      },
+      paddle2: {
+        x: 0, y: 0,          // Set on Physics.init()
+        width: 12, height: 80,
+        speed: 400,
+        color: '#fff'
+      },
+      score1: 0,
+      score2: 0,
+      mode: null,             // null = mode select screen; 'ai' = Solo vs AI; '2p' = 2-Player local
+      difficulty: 'medium',   // 'easy', 'medium', 'hard'
+      gameState: 'modeSelect',// 'modeSelect', 'diffSelect', 'playing', 'scored', 'gameover'
+      winner: null            // null, 'player1', 'player2', 'ai'
     };
 
     const Input = {
-      keys: { w: false, s: false },
+      keys: { w: false, s: false, arrowUp: false, arrowDown: false },
+      _handleKeyDown: null,
+      _handleKeyUp: null,
 
       init() {
-        document.addEventListener('keydown', (e) => {
+        this._handleKeyDown = (e) => {
           if (e.code === 'KeyW')      { this.keys.w         = true;  e.preventDefault(); }
           if (e.code === 'KeyS')      { this.keys.s         = true;  e.preventDefault(); }
-        });
+          if (e.code === 'ArrowUp')   { this.keys.arrowUp   = true;  e.preventDefault(); }
-        document.addEventListener('keyup', (e) => {
+          if (e.code === 'ArrowDown') { this.keys.arrowDown = true;  e.preventDefault(); }
+        };
+        this._handleKeyUp = (e) => {
           if (e.code === 'KeyW')      this.keys.w         = false;
           if (e.code === 'KeyS')      this.keys.s         = false;
-        });
+          if (e.code === 'ArrowUp')   this.keys.arrowUp   = false;
+          if (e.code === 'ArrowDown') this.keys.arrowDown = false;
+        };
+        document.addEventListener('keydown', this._handleKeyDown);
+        document.addEventListener('keyup',   this._handleKeyUp);
       },
 
-      getVerticalInput() {
+      cleanup() {
-        if (this.keys.w) return -1;
+        document.removeEventListener('keydown', this._handleKeyDown);
-        if (this.keys.s) return 1;
+        document.removeEventListener('keyup',   this._handleKeyUp);
-        return 0;
+      },
-      }
+
+      getVerticalInput()  { return this.keys.w ? -1 : this.keys.s ? 1 : 0; },
+      getVerticalInput2() { return this.keys.arrowUp ? -1 : this.keys.arrowDown ? 1 : 0; }
     };
 
     const Physics = {
@@ -134,13 +162,16 @@
         GameState.paddle1.x = 30;
         GameState.paddle1.y = height / 2 - GameState.paddle1.height / 2;
         GameState.paddle1.speed = GameConfig.paddleSpeed;
+        // Position paddle2 on right side, vertically centered
+        GameState.paddle2.x = width - 30 - GameState.paddle2.width;
+        GameState.paddle2.y = height / 2 - GameState.paddle2.height / 2;
+        GameState.paddle2.speed = GameConfig.paddleSpeed;
         // Serve ball from center
         this.serveBall();
       },
 
       onResize(width, height) {
-        this.width = width;
+        this.init(width, height);
-        this.height = height;
       },
 
       serveBall() {