feat!: implemented multigame support (#34)

Reviewed-on: #34
Co-authored-by: Janis <janis.e.20@gmx.de>
Co-committed-by: Janis <janis.e.20@gmx.de>

knockoutwhistweb/app/assets/stylesheets/login.less

@@ -0,0 +1,35 @@
+.login-box {
+  position: fixed; /* changed from absolute to fixed so it centers relative to the viewport */
+  align-items: center;
+  justify-content: center;
+  top: 50%;
+  left: 50%;
+  transform: translate(-50%, -50%); /* center exactly */
+  display: flex;
+  width: 100%;
+  max-width: 420px; /* keeps box from stretching too wide */
+  padding: 1rem;
+  z-index: 2; /* above particles */
+}
+
+.login-card {
+  max-width: 400px;
+  width: 100%;
+  border: none;
+  border-radius: 1rem;
+  box-shadow: 0 4px 20px rgba(0,0,0,0.1);
+  position: relative;
+  z-index: 3; /* ensure card sits above the particles */
+}
+
+#particles-js {
+  position: fixed;
+  top: 0;
+  left: 0;
+  width: 100%;
+  height: 100%;
+  z-index: 0; /* behind content */
+  pointer-events: none; /* allow clicks through particles */
+  background-repeat: no-repeat;
+  background-size: cover;
+}