refactor: remove unused authentication files and dependencies; update package.json to streamline dependencies and improve project structure

apps/web/package.json

@@ -27,14 +27,11 @@
     "vite": "^7.1.2"
   },
   "dependencies": {
-    "@convex-dev/better-auth": "^0.9.6",
     "@dicebear/collection": "^9.2.4",
     "@dicebear/core": "^9.2.4",
     "@internationalized/date": "^3.10.0",
-    "@mmailaender/convex-better-auth-svelte": "^0.2.0",
     "@sgse-app/backend": "*",
     "@tanstack/svelte-form": "^1.19.2",
-    "better-auth": "1.3.27",
     "convex": "^1.28.0",
     "convex-svelte": "^0.0.11",
     "date-fns": "^4.1.0",
@@ -43,4 +40,4 @@
     "jspdf-autotable": "^5.0.2",
     "zod": "^4.0.17"
   }
-}
+}