feat(login): Netzwerk-Muster driftet langsam

Knoten laufen auf eigenen Lissajous-Bahnen, Linien folgen den Knoten.
Positionen werden per requestAnimationFrame direkt am DOM gesetzt, damit
React nicht pro Frame neu rendert. Bei prefers-reduced-motion bleibt das
Muster statisch.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/components/LoginScreen.tsx

@@ -1,30 +1,112 @@
-import React, { useState } from 'react';
+import React, { useEffect, useRef, useState } from 'react';
 import { useAuth } from '../lib/auth';
 
+/**
+ * Knoten des dekorativen Netzwerks. Jeder Knoten driftet auf einer eigenen
+ * Lissajous-Bahn, damit sich das Muster nie exakt wiederholt.
+ */
+const NETWORK_NODES = [
+  { x: 80, y: 300, r: 9, ax: 10, ay: 7, sx: 0.055, sy: 0.041, px: 0.0, py: 1.9 },
+  { x: 150, y: 210, r: 13, ax: 8, ay: 11, sx: 0.037, sy: 0.049, px: 1.2, py: 0.4 },
+  { x: 240, y: 250, r: 10, ax: 12, ay: 8, sx: 0.045, sy: 0.033, px: 2.7, py: 3.3 },
+  { x: 310, y: 150, r: 12, ax: 9, ay: 12, sx: 0.031, sy: 0.052, px: 4.1, py: 1.1 },
+  { x: 250, y: 80, r: 7, ax: 13, ay: 9, sx: 0.048, sy: 0.036, px: 5.4, py: 2.6 },
+  { x: 160, y: 340, r: 6, ax: 11, ay: 10, sx: 0.042, sy: 0.057, px: 0.8, py: 4.8 },
+  { x: 360, y: 240, r: 8, ax: 7, ay: 13, sx: 0.058, sy: 0.029, px: 3.5, py: 0.2 },
+];
+
+/** Verbindungen zwischen den Knoten (Indizes in NETWORK_NODES). */
+const NETWORK_EDGES: Array<[number, number]> = [
+  [0, 1],
+  [1, 2],
+  [2, 3],
+  [3, 4],
+  [4, 1],
+  [0, 5],
+  [5, 2],
+  [3, 6],
+  [6, 2],
+];
+
 /** Dekoratives Netzwerk-Muster - greift das Knoten-Motiv des perinco Logos auf. */
-const NetworkPattern: React.FC = () => (
+const NetworkPattern: React.FC = () => {
+  const circleRefs = useRef<Array<SVGCircleElement | null>>([]);
+  const lineRefs = useRef<Array<SVGLineElement | null>>([]);
+
+  useEffect(() => {
+    const reduced = window.matchMedia('(prefers-reduced-motion: reduce)');
+    if (reduced.matches) return;
+
+    let frame = 0;
+    const start = performance.now();
+
+    const tick = (now: number) => {
+      const t = (now - start) / 1000;
+      const positions = NETWORK_NODES.map((node) => ({
+        x: node.x + Math.sin(t * node.sx * Math.PI * 2 + node.px) * node.ax,
+        y: node.y + Math.cos(t * node.sy * Math.PI * 2 + node.py) * node.ay,
+      }));
+
+      positions.forEach((pos, index) => {
+        const circle = circleRefs.current[index];
+        if (!circle) return;
+        circle.setAttribute('cx', pos.x.toFixed(2));
+        circle.setAttribute('cy', pos.y.toFixed(2));
+      });
+
+      NETWORK_EDGES.forEach(([from, to], index) => {
+        const line = lineRefs.current[index];
+        if (!line) return;
+        line.setAttribute('x1', positions[from].x.toFixed(2));
+        line.setAttribute('y1', positions[from].y.toFixed(2));
+        line.setAttribute('x2', positions[to].x.toFixed(2));
+        line.setAttribute('y2', positions[to].y.toFixed(2));
+      });
+
+      frame = requestAnimationFrame(tick);
+    };
+
+    frame = requestAnimationFrame(tick);
+    return () => cancelAnimationFrame(frame);
+  }, []);
+
+  return (
     <svg
       className="pointer-events-none absolute inset-0 h-full w-full opacity-20"
       viewBox="0 0 400 400"
       fill="none"
       aria-hidden="true"
     >
-    <g stroke="white" strokeWidth="1.2">
-      <path d="M80 300 L150 210 L240 250 L310 150 L250 80 L150 210" />
-      <path d="M80 300 L160 340 L240 250" />
-      <path d="M310 150 L360 240 L240 250" />
+      <g stroke="white" strokeWidth="1.2" strokeLinecap="round">
+        {NETWORK_EDGES.map(([from, to], index) => (
+          <line
+            key={`${from}-${to}`}
+            ref={(element) => {
+              lineRefs.current[index] = element;
+            }}
+            x1={NETWORK_NODES[from].x}
+            y1={NETWORK_NODES[from].y}
+            x2={NETWORK_NODES[to].x}
+            y2={NETWORK_NODES[to].y}
+          />
+        ))}
       </g>
       <g fill="white">
-      <circle cx="80" cy="300" r="9" />
-      <circle cx="150" cy="210" r="13" />
-      <circle cx="240" cy="250" r="10" />
-      <circle cx="310" cy="150" r="12" />
-      <circle cx="250" cy="80" r="7" />
-      <circle cx="160" cy="340" r="6" />
-      <circle cx="360" cy="240" r="8" />
+        {NETWORK_NODES.map((node, index) => (
+          <circle
+            key={`${node.x}-${node.y}`}
+            ref={(element) => {
+              circleRefs.current[index] = element;
+            }}
+            cx={node.x}
+            cy={node.y}
+            r={node.r}
+          />
+        ))}
       </g>
     </svg>
-);
+  );
+};
 
 export const LoginScreen: React.FC = () => {
   const { login } = useAuth();