M0: scaffold SPA + API monorepo

Backend (Django 6.1 + DRF):
- Token auth with a custom User model (register/login/logout/me)
- Library models (MediaItem, MediaLocation) and REST endpoints
- File list/detail with search, rating filter, sorting, pagination
- Multipart upload with optional rating/tags/notes
- Range-aware media serving (video seeking) and ffmpeg thumbnails
- scan_files management command for the watched folder

Frontend (React 19 + Vite + TypeScript):
- Catppuccin Mocha design tokens from the design docs
- App shell, token persistence, protected routes
- Library grid with filters, file detail with custom data editor
- Upload page with per-file progress via XHR
- Dev proxy to the Django API

frontend/src/lib/format.ts

@@ -0,0 +1,20 @@
+export function formatBytes(bytes: number): string {
+  if (!Number.isFinite(bytes) || bytes < 0) return "—";
+  const units = ["B", "KB", "MB", "GB", "TB"];
+  let value = bytes;
+  let unit = 0;
+  while (value >= 1024 && unit < units.length - 1) {
+    value /= 1024;
+    unit += 1;
+  }
+  const digits = value >= 100 || unit === 0 ? 0 : 1;
+  return `${value.toFixed(digits)} ${units[unit]}`;
+}
+
+export function formatDate(value: string): string {
+  return new Date(value).toLocaleDateString(undefined, {
+    year: "numeric",
+    month: "short",
+    day: "numeric",
+  });
+}