Mobile: lighter render path + touch-to-accelerate the plane

Detects mobile via UA + 768 px media query (IS_MOBILE constant) and
flips three knobs:

- Renderer: antialias off, pixelRatio capped at 1.5 (vs 2 on desktop)
- Parcels: spawn every 2.4 s (vs 1.4 s on desktop) to keep clone+
  draw cost down

Adds touch handlers so users without a mouse can speed the plane up:

- touchstart bumps `touchBoost` from 1 to 6 → BASE_SPEED is multiplied
  by 6 each tick while a finger is on the screen
- touchmove also feeds Math.hypot(dx, dy) * MOUSE_BOOST into
  targetProgress, so swiping advances the plane the same way mouse
  motion does on desktop
- touchend / touchcancel reset touchBoost to 1 and clear last-touch
  coordinates

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

js/intro-scene.js

@@ -12,12 +12,20 @@
 import * as THREE from 'three';
 import { GLTFLoader } from 'three/addons/loaders/GLTFLoader.js';
 
+/* ── Détection mobile ──────────────────────────────────────────────────
+   Sur mobile : on coupe l'antialiasing, on plafonne le pixel ratio à
+   1.5 et on espace davantage les spawns de colis pour garder ~60 fps. */
+const IS_MOBILE = /iPhone|iPad|iPod|Android|Mobile/i.test(navigator.userAgent)
+  || window.matchMedia('(max-width: 768px)').matches;
+
 /* ── Renderer & camera ─────────────────────────────────────────────────── */
 const canvas = document.getElementById('three-canvas');
 const renderer = new THREE.WebGLRenderer({
-  canvas, alpha: true, antialias: true, powerPreference: 'high-performance'
+  canvas, alpha: true,
+  antialias: !IS_MOBILE,
+  powerPreference: 'high-performance'
 });
-renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
+renderer.setPixelRatio(Math.min(window.devicePixelRatio, IS_MOBILE ? 1.5 : 2));
 renderer.outputColorSpace = THREE.SRGBColorSpace;
 renderer.toneMapping = THREE.ACESFilmicToneMapping;
 renderer.toneMappingExposure = 1.05;
@@ -72,7 +80,7 @@ loader.load(
    parachute (mêmes parent → même position/rotation/échelle), et placée
    pile au niveau du harnais pour que l'attachement soit lisible.
 */
-const PARCEL_SPAWN_EVERY = 1.4;
+const PARCEL_SPAWN_EVERY = IS_MOBILE ? 2.4 : 1.4;   // moins fréquent sur mobile
 const PARCEL_FALL_SPEED  = 1.4;
 const PARCEL_DRIFT       = 0.45;
 const PARCEL_INITIAL_SCALE = 0.45;
@@ -237,6 +245,38 @@ window.addEventListener('deviceorientation', (e) => {
   mouse.py = Math.max(0, Math.min(1, (e.beta - 20) / 60));
 }, { passive: true });
 
+/* Tactile : tant que le doigt est posé, l'avion accélère (multiplicateur
+   sur BASE_SPEED). Le swipe ajoute aussi du progrès cumulé comme la
+   souris sur desktop. */
+let touchBoost = 1;
+let lastTouchX = null, lastTouchY = null;
+
+window.addEventListener('touchstart', (e) => {
+  touchBoost = 6;
+  if (e.touches[0]) {
+    lastTouchX = e.touches[0].clientX;
+    lastTouchY = e.touches[0].clientY;
+  }
+}, { passive: true });
+
+window.addEventListener('touchmove', (e) => {
+  const t0 = e.touches[0];
+  if (!t0) return;
+  if (lastTouchX !== null) {
+    const dx = t0.clientX - lastTouchX;
+    const dy = t0.clientY - lastTouchY;
+    mouse.targetProgress = Math.min(1, mouse.targetProgress + Math.hypot(dx, dy) * MOUSE_BOOST);
+  }
+  lastTouchX = t0.clientX;
+  lastTouchY = t0.clientY;
+  mouse.px = t0.clientX / window.innerWidth;
+  mouse.py = t0.clientY / window.innerHeight;
+}, { passive: true });
+
+function endTouch() { touchBoost = 1; lastTouchX = lastTouchY = null; }
+window.addEventListener('touchend',    endTouch, { passive: true });
+window.addEventListener('touchcancel', endTouch, { passive: true });
+
 const root = document.documentElement;
 
 /* ── Révélation du CTA ─────────────────────────────────────────────────
@@ -255,8 +295,9 @@ function tick() {
   const dt = Math.min(0.1, t - lastT);  // clamp pour éviter les bonds après onglet en arrière-plan
   lastT = t;
 
-  /* Avance autonome + cible cumulée par la souris, le tout limité à 1 */
+  /* Avance autonome + boost tactile (×6 tant qu'un doigt touche l'écran)
-  mouse.targetProgress = Math.min(1, mouse.targetProgress + BASE_SPEED * dt);
+     + cible cumulée par souris/swipe, le tout limité à 1 */
+  mouse.targetProgress = Math.min(1, mouse.targetProgress + BASE_SPEED * touchBoost * dt);
   /* Lerp doux pour fluidifier */
   mouse.progress += (mouse.targetProgress - mouse.progress) * 0.06;
   const p = mouse.progress;