chore(home): swap Kyoto Animation and Shinkai style thumbnails

Replace the auto-generated kyoani / shinkai style thumbnails with hand-picked
reference frames. Source PNGs were center-cropped to square and re-encoded as
512x512 WEBP (~41KB each) to match the existing thumbnail format. Bumps the
shared cache-buster from v5 to v6 so existing browsers fetch the new files.

app/page.tsx

@@ -870,7 +870,7 @@ function StyleModal({
   const [parsing, setParsing] = useState(false);
   const [parseError, setParseError] = useState<string | null>(null);
   const fileInputRef = useRef<HTMLInputElement>(null);
-  const thumbV = "v5";
+  const thumbV = "v6";
   const STYLE_THUMB: Record<string, string> = {
     "自动": `/home/styles/auto.webp?${thumbV}`,
     "自定义风格": `/home/styles/custom.webp?${thumbV}`,