UX/UI/perf pass: admin tabs, theme toggle, log polish, mod search, JAR cache

- Admin page split into tabs (Server/Players/Chat/Mods/Backups/Logs) with
  hash + localStorage persistence; inactive tabs no longer mount.
- Log viewer: level color-coding, search, level filter chips, auto-scroll
  toggle, copy button, visible-line count.
- Installed mods list: search field + side filter (all/both/server/client)
  with live count; public ModList gets skeleton + empty states and search.
- Theme toggle with no-flash inline init, localStorage + system preference.
- Layout: full OG / Twitter metadata, title template, keywords,
  dual-theme themeColor, metadataBase.
- lib/mods.ts: per-jar mtime+size parse cache (cold 6s -> warm ~45ms on
  /api/mods for the full mod list); cache eviction on mod removal.
- ChatBridge polling eased 3s -> 5s with 2s stale window.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

components/Navbar.tsx

@@ -3,6 +3,7 @@
 import { useSession, signOut } from "next-auth/react";
 import Link from "next/link";
 import { Button } from "@/components/ui/button";
+import { ThemeToggle } from "@/components/ThemeToggle";
 
 export function Navbar() {
   const { data: session } = useSession();
@@ -14,6 +15,7 @@ export function Navbar() {
           HurkiCorgi MC
         </Link>
         <div className="flex items-center gap-1 sm:gap-2">
+          <ThemeToggle />
           {session ? (
             <>
               <Button variant="ghost" size="sm" render={<Link href="/admin" />}>