feat(frontend): add ParticleBackground component with sakura petals and mouse-tracked sparkles

services/frontend/src/widgets/particles/ParticleBackground.tsx

@@ -0,0 +1,163 @@
+import { Sparkles } from "@react-three/drei";
+import { Canvas, type ThreeElement, useFrame, useThree } from "@react-three/fiber";
+import { useEffect, useMemo, useRef, useState } from "react";
+import type * as THREE from "three";
+
+// ─── Sakura petal geometry ───────────────────────────────────────────────────
+
+function createPetalShape() {
+  const shape = new THREE.Shape();
+  // Teardrop/petal shape
+  shape.moveTo(0, 0.5);
+  shape.bezierCurveTo(0.3, 0.3, 0.4, -0.1, 0, -0.5);
+  shape.bezierCurveTo(-0.4, -0.1, -0.3, 0.3, 0, 0.5);
+  return shape;
+}
+
+const petalShape = createPetalShape();
+const petalGeometry = new THREE.ShapeGeometry(petalShape);
+
+// ─── Inner particle scene ────────────────────────────────────────────────────
+
+function Petal({ mouse }: { mouse: React.RefObject<THREE.Vector2 | null> }) {
+  const meshRef = useRef<THREE.Mesh>(null);
+  const initial = useMemo(() => ({
+    x: (Math.random() - 0.5) * 20,
+    y: Math.random() * 20 - 5,
+    z: (Math.random() - 0.5) * 10 - 2,
+    rotSpeed: (Math.random() - 0.5) * 2,
+    driftX: (Math.random() - 0.5) * 0.005,
+    driftZ: (Math.random() - 0.5) * 0.003,
+    hue: 340 + Math.random() * 30, // pink range: 340–370
+    saturation: 60 + Math.random() * 30,
+    lightness: 65 + Math.random() * 20,
+  }), []);
+
+  useFrame((_, delta) => {
+    if (!meshRef.current) return;
+    const mesh = meshRef.current;
+
+    // Slow drift downward
+    mesh.position.y -= delta * 0.3;
+    mesh.position.x += Math.sin(Date.now() * initial.driftX) * 0.002;
+    mesh.position.z += Math.cos(Date.now() * initial.driftZ) * 0.001;
+    mesh.rotation.z += delta * initial.rotSpeed;
+    mesh.rotation.x += delta * initial.rotSpeed * 0.3;
+
+    // Gentle mouse attraction
+    const dx = mouse.current.x * 3 - mesh.position.x;
+    const dy = mouse.current.y * 2 - mesh.position.y;
+    mesh.position.x += dx * 0.0001;
+    mesh.position.y += dy * 0.0001;
+
+    // Reset when out of view
+    if (mesh.position.y < -10) {
+      mesh.position.y = 8;
+      mesh.position.x = (Math.random() - 0.5) * 20;
+      mesh.position.z = (Math.random() - 0.5) * 10 - 2;
+    }
+  });
+
+  return (
+    <mesh
+      ref={meshRef}
+      geometry={petalGeometry}
+      position={[initial.x, initial.y, initial.z]}
+      scale={[0.12, 0.12, 0.12]}
+    >
+      <meshStandardMaterial
+        color={`hsl(${initial.hue}, ${initial.saturation}%, ${initial.lightness}%)`}
+        transparent
+        opacity={0.7}
+        side={THREE.DoubleSide}
+        depthWrite={false}
+      />
+    </mesh>
+  );
+}
+
+function ParticleScene() {
+  const mouse = useRef(new THREE.Vector2(0, 0));
+  const { size } = useThree();
+  const hiddenRef = useRef(false);
+
+  useEffect(() => {
+    const onMouse = (e: MouseEvent) => {
+      // Normalise to -1..1 relative to viewport
+      mouse.current.x = (e.clientX / window.innerWidth) * 2 - 1;
+      mouse.current.y = -(e.clientY / window.innerHeight) * 2 + 1;
+    };
+    window.addEventListener("mousemove", onMouse);
+
+    const onVisibility = () => {
+      hiddenRef.current = document.hidden;
+    };
+    document.addEventListener("visibilitychange", onVisibility);
+
+    return () => {
+      window.removeEventListener("mousemove", onMouse);
+      document.removeEventListener("visibilitychange", onVisibility);
+    };
+  }, []);
+
+  // Petal count depends on viewport width (fewer on mobile)
+  const petalCount = size.width < 640 ? 10 : size.width < 1024 ? 20 : 35;
+  const petals = useMemo(
+    () => Array.from({ length: petalCount }, (_, i) => <Petal key={i} mouse={mouse} />),
+    [petalCount],
+  );
+
+  return (
+    <>
+      {/* Ambient + directional for soft lighting */}
+      <ambientLight intensity={0.6} />
+      <directionalLight position={[5, 5, 5]} intensity={0.3} />
+
+      {/* Petals */}
+      {!hiddenRef.current && petals}
+
+      {/* Sparkles from drei */}
+      <Sparkles
+        count={size.width < 640 ? 15 : 30}
+        scale={12}
+        size={0.8}
+        speed={0.2}
+        color="#7EC8E3"
+        opacity={0.5}
+      />
+    </>
+  );
+}
+
+// ─── Exported component ──────────────────────────────────────────────────────
+
+export function ParticleBackground() {
+  const [reducedMotion, setReducedMotion] = useState(false);
+
+  useEffect(() => {
+    const mq = window.matchMedia("(prefers-reduced-motion: reduce)");
+    setReducedMotion(mq.matches);
+    const handler = (e: MediaQueryListEvent) => setReducedMotion(e.matches);
+    mq.addEventListener("change", handler);
+    return () => mq.removeEventListener("change", handler);
+  }, []);
+
+  if (reducedMotion) return null;
+
+  return (
+    <div
+      className="fixed inset-0 pointer-events-none"
+      aria-hidden="true"
+      style={{ zIndex: -1 }}
+    >
+      <Canvas
+        camera={{ position: [0, 0, 8], fov: 75 }}
+        dpr={[1, 2]}
+        gl={{ antialias: false, alpha: true }}
+        style={{ background: "transparent" }}
+      >
+        <ParticleScene />
+      </Canvas>
+    </div>
+  );
+}