fix: show warning instead of validation error on WIP settings tabs

The Save All Changes button in Admin Settings was triggering a confusing
"Site name and description are required" error when clicked on non-General
tabs because all tabs routed to the /general endpoint which validates
those fields.

Now the saveAllSettings() function checks if the current tab has save
functionality implemented. For WIP tabs (Appearance, Security, Notifications,
Storage), it shows a warning notification explaining that saving is not yet
available for that section.

Fixes #345

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: lane711

packages/core/src/templates/pages/admin-settings.template.ts

@@ -153,6 +153,15 @@ export function renderSettingsPage(data: SettingsPageData): string {
       const currentTab = '${activeTab}';
 
       async function saveAllSettings() {
+        // Tabs with implemented save functionality
+        const saveableTabs = ['general'];
+
+        // Check if current tab supports saving
+        if (!saveableTabs.includes(currentTab)) {
+          showNotification('Saving is not yet available for this settings section. This feature is under development.', 'warning');
+          return;
+        }
+
         // Collect all form data
         const formData = new FormData();