feat(web): make ProgressBar sticky to top of viewport during generation

web/src/components/ProgressBar.tsx

@@ -12,7 +12,7 @@ export default function ProgressBar() {
 
   if (state.phase === "error") {
     return (
-      <div className="border-b border-red-900/40 bg-red-950/30 px-8 py-2.5">
+      <div className="sticky top-0 z-40 border-b border-red-900/40 bg-red-950/80 backdrop-blur-md px-8 py-2.5">
         <span className="label-mono text-red-400">progress error</span>
         <span className="ml-3 text-sm text-red-300/90">{state.message}</span>
       </div>
@@ -37,7 +37,7 @@ export default function ProgressBar() {
       : `Generating · ${fmt(elapsedS)}`;
 
   return (
-    <div className="border-b border-[hsl(var(--ember))]/30 bg-[hsl(var(--ember))]/10 px-8 py-2">
+    <div className="sticky top-0 z-40 border-b border-[hsl(var(--ember))]/30 bg-[hsl(var(--ember))]/15 backdrop-blur-md px-8 py-2">
       <div className="flex items-center gap-4">
         <span className="label-mono text-[hsl(var(--ember))] whitespace-nowrap">
           {label}