chore: remove dead code, unused CSS, unused components, and clean up git tracking

- Remove storage/logs/ and prod.log from git tracking; add to .gitignore
- Remove unused AvatarCarousel and ArticleSlider components
- Remove unused SkeletonTable export from ui.tsx
- Remove unused ChevronDown import from admin layout
- Remove 13 unused CSS classes (icon-base, nav-*, navigation-icon*, .app.dark,
  text-body, transition-base, card-base, admin-info-grid, .coin.*)
- Remove duplicate translation keys (openMenu/closeMenu in en.json)
- Fix admin-bans to use Prisma-generated bans_type enum
- Create shared AdminPageHeader component and formatDate utility
- Add logger and generateRequestId for structured logging
- All 58 tests pass, typecheck clean, build succeeds

src/components/admin/page-header.tsx

@@ -0,0 +1,21 @@
+import type { LucideIcon } from "lucide-react";
+
+interface AdminPageHeaderProps {
+  icon: LucideIcon;
+  title: string;
+  subtitle: string;
+}
+
+export function AdminPageHeader({ icon: Icon, title, subtitle }: AdminPageHeaderProps) {
+  return (
+    <div className="flex items-center gap-3 mb-6">
+      <div className="w-10 h-10 rounded-xl bg-gradient-to-br from-[var(--color-primary)]/20 to-[var(--color-primary)]/5 grid place-items-center">
+        <Icon size={20} className="text-[var(--color-primary)]" />
+      </div>
+      <div>
+        <h1 className="m-0 text-xl font-extrabold text-[var(--color-text)]">{title}</h1>
+        <p className="m-0 text-xs text-[var(--color-text-muted)] mt-0.5">{subtitle}</p>
+      </div>
+    </div>
+  );
+}