UX: Complete remaining page updates with user-friendly text

PLANNER MODULE:
- Ideas: 'Content Ideas' → 'Article Ideas'
- Dashboard: 'Planner Dashboard' → 'Planning Dashboard'
- Keyword Opportunities: 'Keyword Opportunities' → 'Discover Keywords'

LINKER MODULE:
- Content List: 'Link Content' → 'Add Internal Links'
- Dashboard: 'Linker Dashboard' → 'Internal Linking Dashboard'

OPTIMIZER MODULE:
- Content Selector: 'Optimize Content' → 'Improve Your Articles'
- Dashboard: 'Optimizer Dashboard' → 'Optimization Dashboard'

All page titles now use clear, action-oriented language that non-technical
users can easily understand.

frontend/src/pages/Planner/Ideas.tsx

@@ -358,7 +358,7 @@ export default function Ideas() {
   return (
     <>
       <PageHeader 
-        title="Content Ideas" 
+        title="Article Ideas" 
         badge={{ icon: <BoltIcon />, color: 'orange' }}
         navigation={<ModuleNavigationTabs tabs={plannerTabs} />}
         workflowInsights={workflowInsights}