Remove unused bgInkVignette styling and references.

This cleanup removes the bgInkVignette element and its associated styles from the codebase. These changes simplify the component structure and improve maintainability by eliminating unnecessary code.

frontend/src/App.jsx

@@ -389,7 +389,6 @@ export default function App() {
       <div style={styles.loginPage}>
         <div style={styles.bgFixed} aria-hidden="true">
           <div style={styles.bgMap} />
-          <div style={styles.bgInkVignette} />
         </div>
 
         <div style={styles.candleGlowLayer} aria-hidden="true" />
@@ -501,7 +500,6 @@ export default function App() {
     <div style={styles.page}>
       <div style={styles.bgFixed} aria-hidden="true">
         <div style={styles.bgMap} />
-        <div style={styles.bgInkVignette} />
       </div>
 
       <div style={styles.shell}>
@@ -1165,13 +1163,6 @@ const styles = {
     backgroundSize: "cover",
     backgroundPosition: "center",
     backgroundRepeat: "no-repeat",
-
-    /* Blur ist teuer -> aber stabilisieren:
-    filter: "blur(6px) saturate(0.95) contrast(1.05)",
-    transform: "scale(1.06) translateZ(0)",
-    backfaceVisibility: "hidden",
-    willChange: "transform",
-    opacity: 0.95,*/
   },
 
   bgInkVignette: {