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-client/src/routes/+layout.svelte

@@ -23,6 +23,11 @@
     <slot />
   </main>
   
+  <!-- Footer with version -->
+  <footer class="py-4 text-center border-t border-gray-200 bg-white">
+    <p class="text-xs text-gray-400">ServiceManagerWeb v1.6.0 · © 2026 Aduanasoft</p>
+  </footer>
+  
   <!-- Toast notifications -->
   {#each $toast.toasts as toastMessage (toastMessage.id)}
     <Toast