Task #505: Pin the admin "لوحة التحكم" top bar so it stays frozen on iPad

User report: in the admin dashboard on iPad, the top bar (back arrow,
gear icon, "لوحة التحكم" title, mobile menu button) felt like it
detached from the top during scroll — content showed through it and
it didn't look pinned.

Root cause (artifacts/tx-os/src/pages/admin.tsx, line 1148):
the header was `glass-panel ... sticky top-0 z-10`. The `glass-panel`
background is rgba(255,255,255,0.7) — semi-transparent — and z-10 is
low enough that floating elements on the page (os-bg blobs, sidebar
backdrop) bled across it. The sticky positioning itself was correct;
the perception of "not pinned" came from the see-through background.

Fix (single-file CSS-only change, exactly as planned):
- Drop `glass-panel`, replace with inline styles for full control.
- Background: rgba(255,255,255,0.96) — visually opaque so scrolled
  content no longer shows through.
- Keep blur(16px) saturate(160%) (with -webkit- prefix) so the bar
  still has the same soft glass aesthetic.
- z-30 instead of z-10 so nothing in the page overlays it. Modals
  use z-50 so they still cover the bar correctly.
- Add boxShadow 0 4px 20px rgba(15,23,42,0.06) so the bar visibly
  floats above content once scrolling starts.
- Kept `sticky top-0` (not converted to fixed) so the desktop
  sidebar's `top-[73px]` offset still aligns with the bar's bottom.
- Header height unchanged (px-4 py-4 + same children).

No layout changes. No other top bars touched (out of scope).
Existing tx-os tests are unaffected (no logic, only presentation).

artifacts/tx-os/src/pages/admin.tsx

@@ -1145,7 +1145,15 @@ export default function AdminPage() {
   return (
     <div className="min-h-screen os-bg flex flex-col">
       {/* Header */}
-      <div className="glass-panel border-b border-slate-200/70 px-4 py-4 flex items-center gap-3 sticky top-0 z-10">
+      <div
+        className="border-b border-slate-200/70 px-4 py-4 flex items-center gap-3 sticky top-0 z-30"
+        style={{
+          background: "rgba(255,255,255,0.96)",
+          backdropFilter: "blur(16px) saturate(160%)",
+          WebkitBackdropFilter: "blur(16px) saturate(160%)",
+          boxShadow: "0 4px 20px rgba(15,23,42,0.06)",
+        }}
+      >
         <button
           onClick={() => setLocation("/")}
           className="p-2 rounded-xl hover:bg-slate-100 text-muted-foreground hover:text-foreground transition-colors"