UX: Update Planner pages with user-friendly text

- Keywords page: Changed 'Keywords' to 'Your Keywords'
- Clusters page: Changed 'Keyword Clusters' to 'Topic Clusters'
- Shared columns: Changed 'Volume' to 'Search Volume'
- Shared columns: Changed 'Cluster' to 'Topic Group'
- Shared columns: Changed 'Sector' to 'Category'

frontend/src/pages/Planner/Clusters.tsx

@@ -452,7 +452,7 @@ export default function Clusters() {
   return (
     <>
       <PageHeader 
-        title="Keyword Clusters" 
+        title="Topic Clusters" 
         badge={{ icon: <GroupIcon />, color: 'purple' }}
         navigation={<ModuleNavigationTabs tabs={plannerTabs} />}
         workflowInsights={workflowInsights}