Refactor App layout and enhance UI components for better usability

- Changed the default active tab in the App component from 'profiles' to 'main'.
- Improved the layout of the main content area to better accommodate different views, including profiles, generation forms, and history.
- Updated Sidebar component to reflect the new tab structure with a 'main' tab.
- Enhanced the GenerationForm to utilize the selected profile from the UI store, improving user feedback when no profile is selected.
- Added a new CircleButton component for better icon button interactions.
- Adjusted styles in various components for improved responsiveness and visual consistency.

landing/src/components/DownloadSection.tsx

@@ -35,7 +35,7 @@ export function DownloadSection() {
       </div>
       <div className="grid grid-cols-1 md:grid-cols-3 gap-4 sm:gap-6">
         {downloads.map(({ platform, icon: Icon, link, description }) => (
-          <Card key={platform} className="hover:border-primary/50 hover:shadow-xl hover:shadow-primary/10 transition-all duration-300 hover:-translate-y-1">
+          <Card key={platform} className="hover:border-primary/20 hover:shadow-lg hover:shadow-primary/3 transition-all duration-200 hover:-translate-y-0.5">
             <CardContent className="p-6">
               <div className="flex flex-col items-center text-center space-y-4">
                 <div className="p-3 rounded-xl bg-muted/50 backdrop-blur-sm border border-border">