feat: futuristic theme ladder + stacked landing banner

Add three opt-in dark themes (BooCode+, BooCode Classic, BooCode
Override) plus an in-place Ember polish, on a class-scoped effects
engine: matrix rain, a neon grid field, and frosted glass, all gated
by a localStorage "Animated background" toggle and prefers-reduced-
motion. Extend the server theme_id whitelist so the new ids persist,
and replace the Home landing wordmark with the stacked mascot +
wordmark banner.

apps/web/src/pages/Home.tsx

@@ -2,6 +2,8 @@ import { useEffect, useState } from 'react';
 import { ChevronDown, ChevronRight, Folder, FolderTree, Menu, RotateCcw } from 'lucide-react';
 import { toast } from 'sonner';
 import { Button } from '@/components/ui/button';
+import mascot from '@/assets/brand/banner-mascot.png';
+import wordmark from '@/assets/brand/banner-wordmark.png';
 import { AddProjectModal } from '@/components/AddProjectModal';
 import { CreateProjectModal } from '@/components/CreateProjectModal';
 import { api } from '@/api/client';
@@ -117,7 +119,20 @@ export function Home() {
             </>
           ) : (
             <>
-              <h1 className="text-2xl font-semibold tracking-tight">BooCode</h1>
+              <div className="flex flex-col items-center gap-4 pb-1">
+                <img
+                  src={mascot}
+                  alt=""
+                  draggable={false}
+                  className="h-28 w-auto select-none"
+                />
+                <img
+                  src={wordmark}
+                  alt="BooCode"
+                  draggable={false}
+                  className="h-16 w-auto select-none"
+                />
+              </div>
               <p className="text-sm text-muted-foreground">
                 Pick a project from the sidebar, or add another.
               </p>