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/components/Icon.svelte

@@ -11,11 +11,12 @@
 			| 'projects'
 			| 'provider'
 			| 'feishu'
-			| 'menu'
-			| 'logout'
-			| 'org'
-			| 'chevron'
-			| 'folder'
+		| 'menu'
+		| 'logout'
+		| 'org'
+		| 'chevron'
+		| 'arrow-left'
+		| 'folder'
 			| 'file'
 			| 'check';
 		class?: string;
@@ -100,6 +101,14 @@
 	<svg class={className} viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75">
 		<path stroke-linecap="round" stroke-linejoin="round" d="M8.25 4.5l7.5 7.5-7.5 7.5" />
 	</svg>
+{:else if name === 'arrow-left'}
+	<svg class={className} viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75">
+		<path
+			stroke-linecap="round"
+			stroke-linejoin="round"
+			d="M10.5 19.5L3 12m0 0l7.5-7.5M3 12h18"
+		/>
+	</svg>
 {:else if name === 'folder'}
 	<svg class={className} viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75">
 		<path