feat: HR Portal - Complete Multi-Tenant System with Redis Session Storage

Major Features:
- ✅ Multi-tenant architecture (tenant isolation)
- ✅ Employee CRUD with lifecycle management (onboarding/offboarding)
- ✅ Department tree structure with email domain management
- ✅ Company info management (single-record editing)
- ✅ System functions CRUD (permission management)
- ✅ Email account management (multi-account per employee)
- ✅ Keycloak SSO integration (auth.lab.taipei)
- ✅ Redis session storage (10.1.0.254:6379)
  - Solves Cookie 4KB limitation
  - Cross-system session sharing
  - Sliding expiration (8 hours)
  - Automatic token refresh

Technical Stack:
Backend:
- FastAPI + SQLAlchemy
- PostgreSQL 16 (10.1.0.20:5433)
- Keycloak Admin API integration
- Docker Mailserver integration (SSH)
- Alembic migrations

Frontend:
- Next.js 14 (App Router)
- NextAuth 4 with Keycloak Provider
- Redis session storage (ioredis)
- Tailwind CSS

Infrastructure:
- Redis 7 (10.1.0.254:6379) - Session + Cache
- Keycloak 26.1.0 (auth.lab.taipei)
- Docker Mailserver (10.1.0.254)

Architecture Highlights:
- Session管理由 Keycloak + Redis 統一控制
- 支援多系統 (HR/WebMail/Calendar/Drive/Office) 共享 session
- Token 自動刷新,異質服務整合
- 未來可無縫遷移到雲端

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

frontend/components/auth/session-provider.tsx

@@ -0,0 +1,32 @@
+/**
+ * 認證 Session Provider
+ */
+'use client'
+
+import { useEffect } from 'react'
+import { SessionProvider as NextAuthSessionProvider, useSession, signOut } from 'next-auth/react'
+
+/**
+ * Session Monitor - 監控 Keycloak token refresh 狀態
+ */
+function SessionMonitor({ children }: { children: React.ReactNode }) {
+  const { data: session, status } = useSession()
+
+  useEffect(() => {
+    // 如果 session 有 RefreshTokenError，強制登出
+    if (status === 'authenticated' && (session as any)?.error === 'RefreshTokenError') {
+      console.error('[SessionMonitor] Keycloak refresh token expired - forcing logout')
+      signOut({ callbackUrl: '/auth/signin' })
+    }
+  }, [session, status])
+
+  return <>{children}</>
+}
+
+export function SessionProvider({ children }: { children: React.ReactNode }) {
+  return (
+    <NextAuthSessionProvider>
+      <SessionMonitor>{children}</SessionMonitor>
+    </NextAuthSessionProvider>
+  )
+}