feat: migrate from Create React App to Vite

Rebuild the site on the stack the other converted sites share: Vite 8,
React 19, TypeScript 7, react-router 8, Biome and sanitize.css, with the
site data moved out of the bundle into static-contents/.

- base the database and forum code on cerebellum.neuroinf.jp, keeping
  the CBSN item fields for papers, books and presentations
- serve the XooNIps and forum data from modules/, redirecting the old
  download and /database/file URLs
- restate the theme sizes as border-box totals and keep form controls
  on white
- track page views with GA4

src/common/lib/Loading.module.css

@@ -0,0 +1,27 @@
+.container {
+    display: flex;
+    justify-content: center;
+    align-content: center;
+    margin: 100px 0;
+}
+
+.spinner {
+    width: 120px;
+    height: 120px;
+    border: 8px solid #eeeeee;
+    border-top-color: #cccccc;
+    border-radius: 50%;
+    animation: spin 1s linear infinite;
+}
+
+@keyframes spin {
+    to {
+        transform: rotate(360deg);
+    }
+}
+
+@media (prefers-reduced-motion: reduce) {
+    .spinner {
+        animation-duration: 4s;
+    }
+}