feat: add header icons to all dashboard panels

Consistent icon treatment across Pages, Referrers, Locations,
Technology, Campaigns, Peak Hours, Goals, and Search panels.

components/dashboard/Campaigns.tsx

@@ -127,6 +127,7 @@ export default function Campaigns({ siteId, dateRange, filters, onFilter }: Camp
       <div className="bg-white dark:bg-neutral-900 border border-neutral-200 dark:border-neutral-800 rounded-2xl p-6 h-full flex flex-col">
         <div className="flex items-center justify-between mb-4">
           <div className="flex items-center gap-2">
+            <Megaphone className="w-5 h-5 text-neutral-400 dark:text-neutral-500" weight="bold" />
             <h3 className="text-lg font-semibold text-neutral-900 dark:text-white">
               Campaigns
             </h3>