feat: remove glassmorphism from notification toast; improve video player UX

Task 4 — Event Registration Confirmation (glassmorphism removal):
- Replace translucent gradient + backdrop-blur-md toast in use-realtime.tsx
  with a solid bg-card container, full-opacity border, and a colored
  left accent bar — high contrast, readable in all themes, no blur

Task 5 — Video player UX (within anti-cheat constraints):
- Keyboard shortcuts: Space (play/pause), M (mute), ← (seek back 10s),
  F (fullscreen) — active globally, disabled when an input is focused
- Fullscreen button added to the control bar (F key shortcut)
- Volume slider (0–100%) replaces mute-only toggle; volume is persisted
  to localStorage across sessions under key `pargar:volume`
- Buffer range visualized as a translucent white bar behind the playback
  progress track so users see how much is buffered
- Exponential backoff auto-retry on video error: 1s, 2s, 4s … 30s cap;
  retry count shown in error message; manual retry clears the timer
- Speed controls (0.75x–2x) are intentionally absent: the verified-watch
  anti-cheat locks playbackRate=1; changing it would break the heartbeat
  accumulation that gates quiz unlock and certification
- HLS/ABR requires backend FFmpeg transcoding; the player is structured
  so swapping src=mp4 → src=.m3u8 + hls.js is a one-file change when
  the backend pipeline is ready

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

frontend/src/hooks/use-realtime.tsx

@@ -68,16 +68,19 @@ export function useRealtimeGateway() {
                     toast.dismiss(id);
                     if (n.route) router.push(n.route);
                   }}
-                  className="w-[min(22rem,calc(100vw-1.5rem))] rounded-xl border border-primary/40 bg-gradient-to-br from-primary/25 via-primary/12 to-accent/20 px-3 py-2.5 text-start shadow-[0_16px_40px_-16px_color-mix(in_srgb,var(--color-primary)_75%,transparent)] backdrop-blur-md"
+                  className="flex w-[min(22rem,calc(100vw-1.5rem))] items-stretch overflow-hidden rounded-xl border border-border bg-card text-start shadow-lg"
                 >
-                  <span dir="auto" className="block truncate text-sm font-semibold text-foreground [unicode-bidi:plaintext]">
-                    {title}
-                  </span>
-                  {body ? (
-                    <span dir="auto" className="mt-0.5 block line-clamp-2 text-xs text-foreground/75 [unicode-bidi:plaintext]">
-                      {body}
+                  <span className="w-1 shrink-0 bg-primary" aria-hidden />
+                  <span className="flex min-w-0 flex-col px-3 py-2.5">
+                    <span dir="auto" className="block truncate text-sm font-semibold text-foreground [unicode-bidi:plaintext]">
+                      {title}
                     </span>
-                  ) : null}
+                    {body ? (
+                      <span dir="auto" className="mt-0.5 block line-clamp-2 text-xs text-muted-foreground [unicode-bidi:plaintext]">
+                        {body}
+                      </span>
+                    ) : null}
+                  </span>
                 </button>
               ),
               { duration: 5000 },