refactor(admin): CRM을 apps/admin 독립 프로젝트로 분리

- apps/web에서 admin 라우트/가드/sidebar 링크 제거
- apps/admin: 독립 Next.js 앱 (포트 3001)
  - 자체 login/unauthorized/auth callback
  - admin-sidebar: Overview/Users/Subscriptions/Usage
  - requireAdmin() 가드: profile.role='admin' 체크
- monorepo workspace에 apps/admin 등록

apps/web/src/lib/admin-guard.ts

@@ -1,32 +0,0 @@
-// apps/web/src/lib/admin-guard.ts
-// RSC용 admin 가드 — profile.role='admin' 체크, 실패 시 redirect
-
-import { redirect } from 'next/navigation'
-import { getSupabaseServerClient } from './supabase-server'
-
-interface AdminProfile {
-  id: string
-  name: string | null
-  role: string
-}
-
-export async function requireAdmin(): Promise<AdminProfile> {
-  const supabase = await getSupabaseServerClient()
-  const { data: { user } } = await supabase.auth.getUser()
-
-  if (!user) {
-    redirect('/login')
-  }
-
-  const { data: profile } = await supabase
-    .from('profiles')
-    .select('id, name, role')
-    .eq('id', user.id)
-    .maybeSingle()
-
-  if (!profile || (profile as { role: string }).role !== 'admin') {
-    redirect('/dashboard')
-  }
-
-  return profile as AdminProfile
-}