feat(hub): migrate database admin pages to SPA (database-admin)

- scaffold hub/database-admin as SvelteKit 2 + Svelte 5 static SPA
  with aurora/glass visual style (paths.base='/database')
- add lib/{api,session,org}.ts + Aurora.svelte component
- add routes: root redirect, /admin login page, /dashboard (OWNER/ADMIN only)
- backend: replace server-rendered HTML routes with /database/config JSON endpoint
- add hub/src/database/static.ts to serve SPA under /database/*
- wire registerDatabaseSpa into plugin.ts
- exempt /database/* from silo rate-limit (same treatment as /admin/*)
- add database:dev + database:build npm scripts; update deploy scripts
- update hub/src/database/README.md

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

hub/database-admin/src/lib/components/Aurora.svelte

@@ -0,0 +1,6 @@
+<!-- Animated aurora background blobs, shared by both pages (soft pastels on light). -->
+<div class="pointer-events-none fixed inset-0 overflow-hidden">
+	<div class="aurora absolute -left-32 -top-32 h-96 w-96 rounded-full bg-violet-300/50"></div>
+	<div class="aurora absolute right-0 top-1/4 h-96 w-96 rounded-full bg-cyan-300/40" style="animation-delay:-6s"></div>
+	<div class="aurora absolute bottom-0 left-1/3 h-96 w-96 rounded-full bg-indigo-300/40" style="animation-delay:-12s"></div>
+</div>