feat(admin): music library admin + fix CRM analytics UTC

- /admin/music: list / upload / delete studio audio tracks (content-svc
  GET/POST/DELETE /v1/music) — fills the legacy music-library gap
- fix: CRM analytics coerced query-bound dates to UTC (Npgsql timestamptz
  rejects Kind=Unspecified) — endpoint was returning 400

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/[locale]/admin/layout.tsx

@@ -22,6 +22,7 @@ export default async function AdminLayout({
     { href: "/admin/ranking", label: t("ranking") },
     { href: "/admin/tags", label: t("tags") },
     { href: "/admin/fonts", label: t("fonts") },
+    { href: "/admin/music", label: t("music") },
     { href: "/admin/blogs", label: t("blogs") },
     { href: "/admin/slides", label: t("slides") },
     { href: "/admin/files", label: t("media") },