feat(09-04): rewire /admin nested route + guard + Tailwind safelist

- Replace flat /admin route with nested AdminLayout subtree (5 children)
- Fix beforeEach guard to use to.matched.some(r => r.meta.requiresAdmin)
- Add D-09 admin-on-user-route redirect and D-10a non-admin-on-admin redirect
- Add Tailwind safelist covering sky+amber color families (formatters + AuditLogTab)

frontend/tailwind.config.js

@@ -2,6 +2,10 @@
 import forms from '@tailwindcss/forms'
 export default {
   content: ['./index.html', './src/**/*.{vue,js}'],
+  safelist: [
+    { pattern: /bg-(blue|sky|green|purple|orange|amber|gray|indigo|red)-(50|100|500|600)/ },
+    { pattern: /text-(blue|sky|green|purple|orange|amber|gray|indigo|red)-(400|500|600|700)/ },
+  ],
   theme: {
     extend: {},
   },