Fix boss banner sticking behind nav header on scroll

The sticky level cap banner had z-10 and top-0, placing it behind the
nav (z-40) and overlapping it. Use top-14 to clear the nav height and
z-30 to layer correctly below the nav but above page content.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/RunEncounters.tsx

@@ -1053,7 +1053,7 @@ export function RunEncounters() {
 
       {/* Level Cap Bar */}
       {run.rules?.levelCaps && sortedBosses.length > 0 && (
-        <div className="sticky top-0 z-10 bg-surface-0 border border-border-default rounded-lg px-4 py-3 mb-6 shadow-sm">
+        <div className="sticky top-14 z-30 bg-surface-0 border border-border-default rounded-lg px-4 py-3 mb-6 shadow-sm">
           <div className="flex items-center justify-between mb-2">
             <div className="flex items-center gap-3">
               <span className="text-sm font-semibold text-text-primary">