refactor: remove bookshelf route, consolidate to dashboard

- Update header navigation to link to /dashboard instead of /bookshelf
- Update index page auto-redirect to use /dashboard
- Remove duplicate route, keeping full-featured dashboard with filters

templates/index.templ

@@ -128,7 +128,7 @@ templ Index(loggedIn bool) {
 
         <script src="/static/theme.js"></script>
         <script>
-            // Auto-redirect to bookshelf if user is logged in
+            // Auto-redirect to dashboard if user is logged in
             document.addEventListener('DOMContentLoaded', function() {
                 const token = localStorage.getItem('token');
                 if (token) {
@@ -140,8 +140,8 @@ templ Index(loggedIn bool) {
                     })
                     .then(response => {
                         if (response.ok) {
-                            // Token is valid, redirect to bookshelf
-                            window.location.href = '/bookshelf';
+                            // Token is valid, redirect to dashboard
+                            window.location.href = '/dashboard';
                         }
                     })
                     .catch(error => {