Remove gradient text styles from analytics UI

Replaces gradient text styles with solid color classes in AdminAnalytics and updates the .text-gradient utility in globals.css. This simplifies the visual style for headings and revenue display.

components/admin/AdminAnalytics.tsx

@@ -817,7 +817,7 @@ export default function AdminAnalytics() {
 
       <div className="flex flex-col md:flex-row md:items-center justify-between gap-4">
         <div>
-          <h2 className="text-3xl font-bold tracking-tight bg-gradient-to-r from-foreground to-foreground/70 bg-clip-text text-transparent">
+          <h2 className="text-3xl font-bold tracking-tight">
             Dashboard Analytics
             {!isViewingCurrentYear && (
               <span className="ml-2 text-xl font-normal text-muted-foreground/60">
@@ -974,7 +974,7 @@ export default function AdminAnalytics() {
                 <div className="text-sm font-medium text-muted-foreground">
                   Revenue
                 </div>
-                <div className="text-2xl font-bold bg-gradient-to-r from-green-600 to-green-400 bg-clip-text text-transparent">
+                <div className="text-2xl font-bold text-green-600">
                   {formatAdminCurrency(bestMonth.revenue)}
                 </div>
                 <div className="text-sm text-muted-foreground mt-1">