Make HK sidebar menu clearly readable and structured

- Strong, obvious active state: accent-tinted background, bold text,
  accent icon and left accent border so the current section is unmistakable
- Inactive items stay fully readable (white on dark) with a clear hover
- Separate nav sections with dividers and bolder uppercase headers
- Fix invisible mobile hamburger hover (bg-black/10 -> accent tint)

src/components/admin/admin-mobile-wrapper.tsx

@@ -28,7 +28,7 @@ export function AdminMobileWrapper({
         <button
           type="button"
           onClick={() => setOpen(!open)}
-          className="flex items-center justify-center w-9 h-9 rounded-lg transition-colors hover:bg-black/10"
+          className="flex items-center justify-center w-9 h-9 rounded-lg transition-colors hover:bg-[var(--admin-accent)]/15"
           style={{ color: "var(--admin-text-muted)" }}
         >
           {open ? <X size={18} /> : <Menu size={18} />}