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- Removed outdated pages and integrated their functionalities into tabs under Players, Activity, Content, and Settings.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.

README.md

@@ -141,9 +141,9 @@ so both providers pick them up on existing DBs without a new migration
 
 ### Signup codes
 
-When account creation is disabled (admin **Server settings**), the only
+When account creation is disabled (admin **Settings → Server**), the only
 way in is an admin-issued single-use **signup code**: generate one in the
-admin panel's **Signup codes** page (with a descriptor + optional expiry),
+admin panel's **Settings → Signup codes** tab (with a descriptor + optional expiry),
 hand it to the player, and they redeem it on the site's **`/join`** page —
 which creates their account bound to the device their game client
 reported, so the next launch logs straight in.