Configure v1.6.0 display across application

- backend/app/core/config.py: Add APP_VERSION = '1.6.0' setting
- backend/app/main.py: Update health and root endpoints to show APP_VERSION
- frontend-internal/Sidebar.svelte: Add version display in sidebar footer
- frontend-client/+layout.svelte: Add version in page footer
- All endpoints now return both app_version (1.6.0) and api_version (v1)

frontend-internal/src/lib/components/Sidebar.svelte

@@ -178,5 +178,10 @@
         </div>
       </div>
     </div>
+    
+    <!-- Version info -->
+    <div class="px-4 py-2 border-t border-gray-100">
+      <p class="text-xs text-gray-400 text-center">v1.6.0</p>
+    </div>
   </div>
 </div>