Refactor admin UI for consolidated navigation and improved moderation workflow

- Updated Sidebar component to consolidate navigation items under new categories: Moderation, Content, and Operations.
- Removed outdated pages and integrated their functionalities into tabs under Players, Activity, Content, and Settings.
- Introduced new Activity and Content pages to house Audit, Player Logs, Community Board, and Loading Tips with tabbed navigation.
- Created a unified Moderation page combining Players, Bans, and Reports with tabbed navigation.
- Refactored individual pages (e.g., Audit, Bans, CommunityBoard, etc.) to support embedded mode for better integration within modals.
- Added Tabs component for consistent tab navigation across multiple pages.
- Updated README to reflect changes in navigation and settings structure.
- Removed Grants page as it is not yet implemented.

DorkNet.Server/admin-ui/src/pages/SettingsHome.tsx

@@ -0,0 +1,26 @@
+import { Settings } from './Settings';
+import { SignupCodes } from './SignupCodes';
+import { PageHeader } from '../components/PageHeader';
+import { Tabs, useTabParam } from '../components/Tabs';
+
+// Server-wide configuration: runtime toggles plus the single-use signup
+// invite codes (an access-control setting in its own right). Old
+// /signup-codes route redirects here with ?tab=signup.
+export function SettingsHome() {
+  const [tab, setTab] = useTabParam<'server' | 'signup'>('server', ['server', 'signup']);
+  return (
+    <div>
+      <PageHeader title="Settings" blurb="Runtime server toggles and single-use signup invite codes." />
+      <Tabs
+        tabs={[
+          { key: 'server', label: 'Server' },
+          { key: 'signup', label: 'Signup codes' },
+        ]}
+        active={tab}
+        onChange={setTab}
+      />
+      {tab === 'server' && <Settings embedded />}
+      {tab === 'signup' && <SignupCodes embedded />}
+    </div>
+  );
+}