Update omsorgWeb mitarbeiter-app backgrounds to match omsorgapp gradient design

Replace static background image and pseudo-element patterns with modern gradient system using radial and linear gradients, consistent with the new omsorgapp design language.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

omsorgWeb/mitarbeiter-app/app.css

@@ -13,7 +13,25 @@ html{background:#031522}
 body{
   margin:0;min-height:100vh;color:var(--text);
   font-family:Arial,Helvetica,sans-serif;line-height:1.45;
-  background:#031522;
+  background:
+    radial-gradient(
+      circle at 15% 10%,
+      rgba(16, 215, 230, 0.22),
+      transparent 33%
+    ),
+    radial-gradient(
+      circle at 85% 85%,
+      rgba(18, 88, 99, 0.32),
+      transparent 38%
+    ),
+    linear-gradient(
+      135deg,
+      #031522 0%,
+      #032a36 38%,
+      #0a3a47 68%,
+      #031522 100%
+    );
+  background-attachment:fixed;
 }
 a{color:inherit;text-decoration:none}
 img{display:block;max-width:100%}