Add toggleable rules panel to Tents game

- Introduce a slide-in "How to Play" panel listing the four Tents rules,
  kept in sync with the engine's own rule comment so the UI can't drift.
- Add a Rules button in the HUD parked where the panel's Close button will
  appear, so opening reads as one control morphing rather than two controls.
- Animate the panel open/close and swap visibility/interactivity between the
  Rules and Close buttons to avoid stacking both in the same spot.

src/games/tents/TentsGame.js

@@ -13,6 +13,16 @@ import {
 
 const FONT_D = 'Righteous';
 const FONT_B = '"Julius Sans One"';
+const RULES_W = 420;
+
+// The same four rules the engine enforces (TentsLogic.js rule comment) —
+// kept here as plain strings so the panel can never drift from the model.
+const RULES_TEXT = [
+  'Every tent must sit next to a tree — up, down, left, or right (no diagonals).',
+  "It's a one-to-one pairing: each tree gets exactly one tent, and each tent belongs to exactly one tree.",
+  'Tents can never touch another tent, not even corner to corner.',
+  'The numbers along the top and side are the exact tent count for that column and row — no more, no less.',
+];
 
 // ── Color helpers (day → night lerps drive the whole scene) ─────────────────
 
@@ -75,6 +85,7 @@ export default class TentsGame extends Phaser.Scene {
     this.sky = { t: 0 };          // 0 = midday, 1 = starry night
     this.won = false;
     this.winPanelShown = false;
+    this.rulesOpen = false;
     this.difficulty = 'porch';
     this.hover = null;           // {c, r}
     this.embers = [];
@@ -107,6 +118,7 @@ export default class TentsGame extends Phaser.Scene {
 
     this.buildHud();
     this.hudLayer.setVisible(false);
+    this.buildRulesPanel();
     this.buildSelectScreen();
 
     this.events.on('shutdown', () => {
@@ -209,7 +221,14 @@ export default class TentsGame extends Phaser.Scene {
     this.btnReset = mk('Reset Tents', 700, () => this.resetTents(), 'ghost');
     this.btnMenu = mk('Menu', 780, () => this.scene.start('GameMenu'), 'ghost');
 
-    this.hudLayer.add([this.btnNew, this.btnAnswer, this.btnReset, this.btnMenu]);
+    // Parked at the same screen position the rules panel's Close button sits
+    // at once open (GAME_WIDTH - RULES_W/2, GAME_HEIGHT - 80), so opening the
+    // panel reads as this button "becoming" Close rather than two separate
+    // controls.
+    this.btnRules = new Button(this, GAME_WIDTH - RULES_W / 2, GAME_HEIGHT - 80, 'Rules',
+      () => this.toggleRules(), { width: 200, height: 56, variant: 'ghost' }).setDepth(31);
+
+    this.hudLayer.add([this.btnNew, this.btnAnswer, this.btnReset, this.btnMenu, this.btnRules]);
   }
 
   makeText(str, x, y, font, size, color) {
@@ -219,6 +238,68 @@ export default class TentsGame extends Phaser.Scene {
     }).setOrigin(0, 0).setDepth(30);
   }
 
+  // ── Rules panel (toggled in-play; parked off-screen until opened) ──────────
+
+  buildRulesPanel() {
+    const panel = this.add.container(GAME_WIDTH, 0).setDepth(35);
+
+    const bg = this.add.graphics();
+    bg.fillStyle(0x101024, 0.95);
+    bg.fillRect(0, 0, RULES_W, GAME_HEIGHT);
+    bg.lineStyle(3, 0xffc46a, 0.9);
+    bg.lineBetween(0, 0, 0, GAME_HEIGHT);
+    panel.add(bg);
+
+    // Pushed down ~100px so the title doesn't sit under the soundtrack
+    // controls (MusicPlayer's skip/mute buttons + track name) in the
+    // top-right corner, which render above this panel's depth.
+    panel.add(this.add.text(RULES_W / 2, 150, 'How to Play', {
+      fontFamily: FONT_D, fontSize: '36px', color: '#ffd76a',
+      stroke: '#3a2a14', strokeThickness: 6,
+    }).setOrigin(0.5));
+
+    let y = 218;
+    RULES_TEXT.forEach((line, i) => {
+      panel.add(this.add.text(24, y, `${i + 1}.`, {
+        fontFamily: FONT_D, fontSize: '22px', color: '#ffd76a',
+      }).setOrigin(0, 0));
+      const body = this.add.text(58, y, line, {
+        fontFamily: FONT_B, fontSize: '20px', color: '#fdf6e3',
+        wordWrap: { width: RULES_W - 82 }, lineSpacing: 4,
+      }).setOrigin(0, 0);
+      panel.add(body);
+      y += body.height + 34;
+    });
+
+    const closeBtn = new Button(this, RULES_W / 2, GAME_HEIGHT - 80, 'Close',
+      () => this.toggleRules(), { width: 200, height: 56, variant: 'ghost' });
+    panel.add(closeBtn);
+
+    this.rulesPanel = panel;
+  }
+
+  toggleRules() {
+    this.rulesOpen = !this.rulesOpen;
+    this.tweens.add({
+      targets: this.rulesPanel,
+      x: this.rulesOpen ? GAME_WIDTH - RULES_W : GAME_WIDTH,
+      duration: 220,
+      ease: 'Quad.Out',
+    });
+    // The panel's own Close button sits in this same screen spot once open,
+    // so hide (and un-click) the Rules button rather than stacking both.
+    this.btnRules.setVisible(!this.rulesOpen);
+    if (this.rulesOpen) {
+      this.btnRules.disableInteractive();
+    } else {
+      this.btnRules.setInteractive({
+        useHandCursor: true,
+        hitArea: new Phaser.Geom.Rectangle(0, 0, 200, 56),
+        hitAreaCallback: Phaser.Geom.Rectangle.Contains,
+      });
+    }
+  }
+
   // ── Select screen ──────────────────────────────────────────────────────────
 
   buildSelectScreen() {