fix: Synology SSO Implicit Grant 방식으로 변경

- response_type: code → token
- redirect_uri: /api/... → /auth/... (프론트엔드 페이지)
- 프론트엔드 callback 페이지 추가 (hash fragment 파싱)
- verify API 추가 (access_token 검증)

server/api/auth/synology/index.get.ts

@@ -16,7 +16,7 @@ export default defineEventHandler(async (event) => {
   
   // Synology SSO Server OAuth 인증 URL
   const authUrl = new URL(`${config.synologyServerUrl}/webman/sso/SSOOauth.cgi`)
-  authUrl.searchParams.set('response_type', 'code')
+  authUrl.searchParams.set('response_type', 'token')
   authUrl.searchParams.set('app_id', config.synologyClientId)
   authUrl.searchParams.set('redirect_uri', config.synologyRedirectUri)
   authUrl.searchParams.set('scope', 'user_id')