Add BYOC page, admin section, and is_byoc team visibility gating

- Frontend: BYOC hosts page (/dashboard/byoc) with register/delete flows,
  shimmer loading, pulsing online status, animated token reveal checkmark
- Frontend: Admin section (/admin/hosts) with platform + BYOC tabs, stat
  pills, skeleton loading, slide-in animations for new rows
- Frontend: AdminSidebar component with accent top bar and admin pill badge
- Frontend: BYOC nav item shown only when team.is_byoc is true (derived
  from teams store, not JWT); disabled for members
- Frontend: Admin shield button in Sidebar, visible only to platform admins
- Backend: is_admin in JWT claims + requireAdmin middleware (DB-validated)
- Backend: is_byoc added to teamResponse so frontend derives visibility
  from fresh team data rather than stale JWT fields
- Backend: SetBYOC admin endpoint (PUT /v1/admin/teams/{id}/byoc)
- Backend: Admin hosts list enriches BYOC entries with team_name
- Host agent: load .env file via godotenv on startup

frontend/src/lib/components/icons/IconShield.svelte

@@ -0,0 +1,18 @@
+<script lang="ts">
+	let { size = 18, class: className = '' }: { size?: number; class?: string } = $props();
+</script>
+
+<svg
+	width={size}
+	height={size}
+	viewBox="0 0 24 24"
+	fill="none"
+	stroke="currentColor"
+	stroke-width="1.75"
+	stroke-linecap="round"
+	stroke-linejoin="round"
+	class={className}
+	aria-hidden="true"
+>
+	<path d="M12 22s8-4 8-10V5l-8-3-8 3v7c0 6 8 10 8 10z" />
+</svg>