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>

backend/test_seq_simple.py

@@ -0,0 +1,63 @@
+import psycopg2
+
+conn = psycopg2.connect('postgresql://admin:DC1qaz2wsx@10.1.0.20:5433/hr_portal')
+cur = conn.cursor()
+
+print('=' * 80)
+print('租戶內序號測試結果')
+print('=' * 80)
+
+# 查看員工序號
+print('\n【員工序號分佈】')
+cur.execute('''
+    SELECT tenant_id, seq_no, employee_id, legal_name
+    FROM tenant_employees
+    ORDER BY tenant_id, seq_no
+    LIMIT 20
+''')
+
+current_tenant = None
+for row in cur.fetchall():
+    if row[0] != current_tenant:
+        current_tenant = row[0]
+        print(f'\n租戶 {row[0]}:')
+    print(f'  seq_no={row[1]:3d} | employee_id={row[2]:8s} | {row[3]}')
+
+# 統計
+print('\n' + '=' * 80)
+print('【租戶序號統計】')
+print('=' * 80)
+cur.execute('''
+    SELECT
+        tenant_id,
+        COUNT(*) as total,
+        MIN(seq_no) as min_seq,
+        MAX(seq_no) as max_seq
+    FROM tenant_employees
+    GROUP BY tenant_id
+    ORDER BY tenant_id
+''')
+
+print('\n租戶ID | 員工數 | 最小序號 | 最大序號')
+print('-' * 50)
+for row in cur.fetchall():
+    print(f'{row[0]:7d} | {row[1]:6d} | {row[2]:8d} | {row[3]:8d}')
+
+# 查看觸發器
+print('\n' + '=' * 80)
+print('【資料庫觸發器】')
+print('=' * 80)
+cur.execute('''
+    SELECT trigger_name, event_object_table
+    FROM information_schema.triggers
+    WHERE trigger_schema = 'public'
+      AND trigger_name LIKE '%seq_no%'
+    ORDER BY event_object_table
+''')
+
+print('\n觸發器名稱                                目標表')
+print('-' * 60)
+for row in cur.fetchall():
+    print(f'{row[0]:40s} {row[1]}')
+
+conn.close()