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-lock.json

@@ -8,6 +8,7 @@
       "name": "sales-trainer-frontend",
       "version": "0.1.0",
       "dependencies": {
+        "lucide-vue-next": "^1.0.0",
         "vue": "^3.4.0",
         "vue-router": "^4.3.0"
       },
@@ -1071,6 +1072,16 @@
         "node": "^8.16.0 || ^10.6.0 || >=11.0.0"
       }
     },
+    "node_modules/lucide-vue-next": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/lucide-vue-next/-/lucide-vue-next-1.0.0.tgz",
+      "integrity": "sha512-V6SPvx1IHTj/UY+FrIYWV5faISsPSb8BnWSFDxAtezWKvWc9ZZ40PDrdu1/Qb5vg4lHWr1hs1BAMGVGm6V1Xdg==",
+      "deprecated": "Package deprecated. Please use @lucide/vue instead.",
+      "license": "ISC",
+      "peerDependencies": {
+        "vue": ">=3.0.1"
+      }
+    },
     "node_modules/magic-string": {
       "version": "0.30.21",
       "resolved": "https://registry.npmjs.org/magic-string/-/magic-string-0.30.21.tgz",