ui(icons): replace colored emoji with modern single-color line icons (lucide-vue-next)

Add lucide-vue-next (stroke-based, single-color, currentColor) and swap emoji icons
across nav + all main views: Settings/LogOut (App), BarChart3/Users/Plus (Analytics),
LayoutDashboard (MyBoard), Sparkles/Users/Pencil (GroupEdit), Box/ListChecks/Paperclip/
PlusCircle/ArrowLeft (GroupBuilder), Target/ArrowLeft/Search (Chat/Personas/Training),
User/Lock/Globe (Settings), Users/UserPlus/Info (AdminUsers).
- Buttons become inline-flex for icon+text alignment.
- Icons inherit currentColor (single color, modern line style).
- Rebuild dist with lucide.

frontend/package.json

@@ -9,6 +9,7 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "lucide-vue-next": "^1.0.0",
     "vue": "^3.4.0",
     "vue-router": "^4.3.0"
   },