feat: Improve UI layout and user experience

- Restructure index page to show welcome section only when IMAP is not configured
- Move stats and search sections to display only after IMAP setup
- Update header text color to neutral for better contrast
- Enhance welcome section with larger button and privacy assurance
- Add shield icon to emphasize data privacy protection

app/templates/partials/welcome_section.html

@@ -6,16 +6,16 @@
     </div>
     <p class="text-base-content/80 mb-4">Ready to tame your email chaos? Let's get your email folders synchronized so we can start organizing your emails with AI-powered rules!</p>
     <div class="flex items-center space-x-4" data-loading-states>
-        <button class="btn btn-primary" hx-get="/api/imap/config" hx-target="#modal-holder"
+        <button class="btn btn-primary btn-lg" hx-get="/api/imap/config" hx-target="#modal-holder"
             hx-swap="innerHTML"
             data-loading-disable>
-            <i class="fas fa-cog mr-2" data-loading-class="!hidden"></i>
             <span data-loading-class="!hidden">Set Up IMAP Sync</span>
+            <i class="fas fa-arrow-right mr-2" data-loading-class="!hidden"></i>
             <span class="loading loading-spinner loading-xs hidden" data-loading-class-remove="hidden"></span>
         </button>
-        <div class="text-sm text-base-content/60">
-            <i class="fas fa-info-circle mr-1"></i>
-            Connect your email account to get started
-        </div>
     </div>
+    <p class="text-sm text-base-content/60 mt-2">
+        <i class="fas fa-shield-alt text-green-500 mr-1"></i>
+        <strong>Your privacy matters!</strong> We never store email content at rest.
+    </p>
 </div>