feat(03-01): replace Paperclip icon with Box in CompanyRail, use VOCAB in Auth

- CompanyRail: import Box from lucide-react instead of Paperclip
- CompanyRail: render <Box> icon instead of <Paperclip> in top rail
- Auth.tsx: import VOCAB from @paperclipai/branding
- Auth.tsx: use VOCAB.appName for logo text and sign-in/create-account headings

ui/src/components/CompanyRail.tsx

@@ -1,5 +1,5 @@
 import { useCallback, useEffect, useMemo, useState } from "react";
-import { Paperclip, Plus } from "lucide-react";
+import { Box, Plus } from "lucide-react";
 import { useQueries } from "@tanstack/react-query";
 import {
   DndContext,
@@ -269,9 +269,9 @@ export function CompanyRail() {
 
   return (
     <div className="flex flex-col items-center w-[72px] shrink-0 h-full bg-background border-r border-border">
-      {/* Paperclip icon - aligned with top sections (implied line, no visible border) */}
+      {/* Nexus icon */}
       <div className="flex items-center justify-center h-12 w-full shrink-0">
-        <Paperclip className="h-5 w-5 text-foreground" />
+        <Box className="h-5 w-5 text-foreground" />
       </div>
 
       {/* Company list */}

ui/src/pages/Auth.tsx

@@ -1,4 +1,5 @@
 import { useEffect, useMemo, useState } from "react";
+import { VOCAB } from "@paperclipai/branding";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { useNavigate, useSearchParams } from "@/lib/router";
 import { authApi } from "../api/auth";
@@ -75,11 +76,11 @@ export function AuthPage() {
         <div className="w-full max-w-md mx-auto my-auto px-8 py-12">
           <div className="flex items-center gap-2 mb-8">
             <Sparkles className="h-4 w-4 text-muted-foreground" />
-            <span className="text-sm font-medium">Paperclip</span>
+            <span className="text-sm font-medium">{VOCAB.appName}</span>
           </div>
 
           <h1 className="text-xl font-semibold">
-            {mode === "sign_in" ? "Sign in to Paperclip" : "Create your Paperclip account"}
+            {mode === "sign_in" ? `Sign in to ${VOCAB.appName}` : `Create your ${VOCAB.appName} account`}
           </h1>
           <p className="mt-1 text-sm text-muted-foreground">
             {mode === "sign_in"