feat: admin-ui UX pass — tooltips, session-expiry redirect, empty states

[jlc488]

A usability pass on the admin console, from issues hit while operating it.

Action tooltips

Every icon-only action button now shows a hover tooltip (PrimeVue Tooltip directive, mirroring the existing aria-labels) — on every list page's row actions and the header. No more guessing what each icon does.

Session-expiry → login

The JWT exp is now honored. An expired token is treated as logged-out, so:

• the router guard bounces the user to /login with a "session expired" notice (instead of leaving them on pages that silently 403);
• the axios interceptor handles 401 and 403-from-an-expired-token. A genuine 403 (valid token, missing permission) is left alone so the view can show "no permission".

(Background: the kit returns 403 for an expired/anonymous token, so a status-only check wasn't enough — the client now decodes exp.)

Empty states

A reusable EmptyState (icon + message) replaces the bare "no results" line on the Users / Roles / Permissions / Groups / Menus lists.

Admin-ui only — no backend change. Built green (vue-tsc + vite).

---

요약 (한국어)

• 액션 툴팁: 아이콘만 있던 모든 행 액션 버튼에 호버 툴팁(무엇을 하는지 바로 보임).
• 세션 만료 → 로그인: JWT exp 인식 → 만료 토큰은 로그아웃 취급, 가드/인터셉터가 로그인으로 보냄("세션 만료" 안내). 정상 403(권한 없음)은 그대로 둠.
• 빈 상태: 재사용 EmptyState(아이콘+메시지)로 리스트 빈 화면 개선.

백엔드 변경 없음, 빌드 그린.