fix(admin-web): break /admin/login returnTo redirect loop in dev

vite dev only proxied /api and /auth, so /admin/login hit the SPA root
layout, re-ran loadSession, got 401, and redirected back to /admin/login
with an ever-nesting returnTo. Proxy /admin/login to the backend (which
owns it before the SPA fallback) and guard redirectToLogin against
re-entering /admin/login.

Replace the only emoji-as-icon (the back-arrow on project detail) with
the Icon component (new arrow-left glyph).

Add scripts/dev-bootstrap.ts for seeding a local Silo (stub probes) so
npm run dev can start on a fresh dev DB.

hub/admin-web/src/lib/session.ts

@@ -52,6 +52,7 @@ export function resolveLoginOrgSlug(): string | null {
 }
 
 export function redirectToLogin(): void {
+	if (window.location.pathname === '/admin/login') return;
 	const ret = encodeURIComponent(
 		window.location.pathname + window.location.search + window.location.hash,
 	);