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/admin/src/lib/supabase-server.ts

@@ -0,0 +1,30 @@
+// apps/admin/src/lib/supabase-server.ts
+// RSC/route handler용 Supabase 클라이언트 (쿠키 기반 세션)
+
+import { cookies } from 'next/headers'
+import { createServerClient, type CookieOptions } from '@supabase/ssr'
+import type { Database } from '@d3ro/api-client'
+
+export async function getSupabaseServerClient(): Promise<ReturnType<typeof createServerClient<Database>>> {
+  const cookieStore = await cookies()
+
+  const url = process.env.NEXT_PUBLIC_SUPABASE_URL ?? ''
+  const key = process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY ?? ''
+
+  return createServerClient<Database>(url, key, {
+    cookies: {
+      getAll() {
+        return cookieStore.getAll()
+      },
+      setAll(cookiesToSet: Array<{ name: string; value: string; options: CookieOptions }>) {
+        try {
+          cookiesToSet.forEach(({ name, value, options }) => {
+            cookieStore.set(name, value, options)
+          })
+        } catch {
+          // RSC에서 set은 실패 가능
+        }
+      }
+    }
+  })
+}