refactor(templates): add error toast support to page templates

Update all page templates to accept an optional error message parameter
and display it via the ErrorToast component when data loading fails.

templates/conflicts.templ

@@ -2,7 +2,7 @@ package templates
 
 import "bookhoard/internal/handlers"
 
-templ Conflicts(user User, conflicts []handlers.ConflictDetailResponse, total int, unresolved int) {
+templ Conflicts(user User, conflicts []handlers.ConflictDetailResponse, total int, unresolved int, errorMessage string) {
     <!DOCTYPE html>
     <html lang="en">
     <head>
@@ -232,6 +232,8 @@ templ Conflicts(user User, conflicts []handlers.ConflictDetailResponse, total in
         </div>
 
         <script src="/static/conflicts.js"></script>
+
+        @ErrorToast(errorMessage)
     </body>
     </html>
 }