feat(backend): Phase 1-4 全新開發完成，37/37 TDD 通過

[Phase 0 Reset]
- 清除舊版 app/、alembic/versions/、雜亂測試腳本
- 新 requirements.txt (移除 caldav/redis/keycloak-lib，加入 apscheduler/croniter/docker/paramiko/ping3/dnspython)

[Phase 1 資料庫]
- 9 張資料表 SQLAlchemy Models：tenants / accounts / schedules / schedule_logs /
  tenant_schedule_results / account_schedule_results / servers / server_status_logs / system_status_logs
- Alembic migration 001_create_all_tables (已套用到 10.1.0.20:5433/virtual_mis)
- seed.py：schedules 初始 3 筆 / servers 初始 4 筆

[Phase 2 CRUD API]
- GET/POST/PUT/DELETE: /api/v1/tenants / accounts / servers / schedules
- /api/v1/system-status
- 帳號編碼自動產生 (prefix + seq_no 4碼左補0)
- 燈號 (lights) 從最新排程結果取得

[Phase 3 Watchdog]
- APScheduler interval 3分鐘，原子 UPDATE status=Going 防重複執行
- 手動觸發 API: POST /api/v1/schedules/{id}/run

[Phase 4 Service Clients]
- KeycloakClient：vmis-admin realm，REST API (不用 python-keycloak)
- MailClient：Docker Mailserver @ 10.1.0.254:8080，含 MX DNS 驗證
- DockerClient：docker-py 本機 + paramiko SSH 遠端 compose
- NextcloudClient：OCS API user/quota
- SystemChecker：功能驗證 (traefik routers>0 / keycloak token / SMTP EHLO / DB SELECT 1 / ping)

[TDD]
- 37 tests / 37 passed (2.11s)
- SQLite in-memory + StaticPool，無需外部 DB

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/services/scheduler/schedule_system.py

@@ -0,0 +1,94 @@
+"""
+Schedule 3 — 系統狀態（每日 08:00）
+Part A: 基礎設施服務功能驗證（traefik/keycloak/mail/db）
+Part B: 伺服器 ping 檢查
+"""
+import logging
+from datetime import datetime
+from sqlalchemy.orm import Session
+
+from app.models.server import SystemStatusLog, ServerStatusLog, Server
+
+logger = logging.getLogger(__name__)
+
+# Fixed 8 services: environment × service_name
+SERVICES = [
+    {"environment": "test", "service_name": "traefik",
+     "service_desc": "測試環境反向代理", "host": "localhost", "port": 8080},
+    {"environment": "test", "service_name": "keycloak",
+     "service_desc": "測試環境 SSO",
+     "url": "https://auth.lab.taipei", "realm": "master"},
+    {"environment": "test", "service_name": "mail",
+     "service_desc": "測試環境 Mail Server", "host": "localhost", "port": 587},
+    {"environment": "test", "service_name": "db",
+     "service_desc": "10.1.0.20:5433 PostgreSQL",
+     "db_host": "10.1.0.20", "db_port": 5433},
+    {"environment": "prod", "service_name": "traefik",
+     "service_desc": "正式環境反向代理", "host": "localhost", "port": 8080},
+    {"environment": "prod", "service_name": "keycloak",
+     "service_desc": "正式環境 SSO",
+     "url": "https://auth.ease.taipei", "realm": "master"},
+    {"environment": "prod", "service_name": "mail",
+     "service_desc": "正式環境 Mail Server", "host": "10.1.0.254", "port": 587},
+    {"environment": "prod", "service_name": "db",
+     "service_desc": "10.1.0.254:5432 PostgreSQL",
+     "db_host": "10.1.0.254", "db_port": 5432},
+]
+
+
+def run_system_status(schedule_log_id: int, db: Session):
+    from app.services.system_checker import SystemChecker
+    checker = SystemChecker()
+
+    # Part A: Infrastructure services
+    for svc in SERVICES:
+        result = False
+        fail_reason = None
+        try:
+            if svc["service_name"] == "traefik":
+                result = checker.check_traefik(svc["host"], svc["port"])
+            elif svc["service_name"] == "keycloak":
+                result = checker.check_keycloak(svc["url"], svc["realm"])
+            elif svc["service_name"] == "mail":
+                result = checker.check_smtp(svc["host"], svc["port"])
+            elif svc["service_name"] == "db":
+                result = checker.check_postgres(svc["db_host"], svc["db_port"])
+        except Exception as e:
+            result = False
+            fail_reason = str(e)
+
+        db.add(SystemStatusLog(
+            schedule_log_id=schedule_log_id,
+            environment=svc["environment"],
+            service_name=svc["service_name"],
+            service_desc=svc["service_desc"],
+            result=result,
+            fail_reason=fail_reason,
+            recorded_at=datetime.utcnow(),
+        ))
+
+    # Part B: Server ping
+    servers = db.query(Server).filter(Server.is_active == True).order_by(Server.sort_order).all()
+    for server in servers:
+        response_time = None
+        fail_reason = None
+        try:
+            response_time = checker.ping_server(server.ip_address)
+            result = response_time is not None
+            if not result:
+                fail_reason = "No response"
+        except Exception as e:
+            result = False
+            fail_reason = str(e)
+
+        db.add(ServerStatusLog(
+            schedule_log_id=schedule_log_id,
+            server_id=server.id,
+            result=result,
+            response_time=response_time,
+            fail_reason=fail_reason,
+            recorded_at=datetime.utcnow(),
+        ))
+
+    db.commit()
+    logger.info(f"System status check done: {len(SERVICES)} services + {len(servers)} servers")