refactor: convert admin panel to Tailwind CSS

- Convert admin layout, sidebar, and navigation to Tailwind classes
- Convert dashboard components (StatusCard, DiagnosticRow, etc.) to Tailwind
- Convert all ~48 admin page files from admin CSS classes to Tailwind
- Remove unused admin CSS from globals.css (973 → 712 lines)
- Convert developers page badges to Tailwind
- Remove <style jsx> block from OnlineUsersWidget

src/app/admin/rare-values/page.tsx

@@ -46,7 +46,7 @@ export default async function AdminRareValues() {
         rendered as a tab on the public rare values page.
       </p>
 
-      <div className="admin-stats">
+      <div className="grid grid-cols-[repeat(auto-fit,minmax(180px,1fr))] gap-3.5 mb-6">
         <StatusCard label="Categories" value={categories.length} icon="🗂️" />
         <StatusCard label="Rare items" value={values.length} icon="💎" />
       </div>
@@ -82,8 +82,8 @@ export default async function AdminRareValues() {
               >
                 <div style={{ display: "flex", gap: "0.6rem", alignItems: "baseline", flexWrap: "wrap" }}>
                   <strong>{cat.name}</strong>
-                  <span className="admin-badge">badge {cat.badge}</span>
-                  <span className="admin-badge">priority {cat.priority}</span>
+                  <span className="inline-block text-[0.72rem] font-bold px-2 py-0.5 rounded-full bg-[var(--color-primary)]/18 text-[var(--color-text)]">badge {cat.badge}</span>
+                  <span className="inline-block text-[0.72rem] font-bold px-2 py-0.5 rounded-full bg-[var(--color-primary)]/18 text-[var(--color-text)]">priority {cat.priority}</span>
                   <span className="muted">{rows.length} item{rows.length === 1 ? "" : "s"}</span>
                 </div>
                 <form action={deleteCategory}>
@@ -112,7 +112,7 @@ export default async function AdminRareValues() {
                       <td>{v.creditValue ?? "—"}</td>
                       <td>{v.currencyValue ?? "—"}</td>
                       <td>
-                        <span className="admin-badge">{v.currencyType}</span>
+                        <span className="inline-block text-[0.72rem] font-bold px-2 py-0.5 rounded-full bg-[var(--color-primary)]/18 text-[var(--color-text)]">{v.currencyType}</span>
                       </td>
                       <td className="muted">{v.furnitureIcon}</td>
                       <td>