feat(vmis): 租戶自動開通完整流程 + Admin Portal SSO + NC 行事曆訂閱

Backend:
- schedule_tenant: NC 新容器自動 pgsql 安裝 (_nc_db_check 全新容器處理)
- schedule_tenant: NC 初始化加入 Redis + APCu memcache 設定 (修正 OIDC invalid_state)
- schedule_tenant: 新租戶 KC realm 自動設定 accessCodeLifespan=600s (修正 authentication_expired)
- schedule_account: NC Mail 帳號自動設定 (nc_mail_result/nc_mail_done_at)
- schedule_account: NC 台灣國定假日行事曆自動訂閱 (CalDAV MKCALENDAR)
- nextcloud_client: 新增 subscribe_calendar() CalDAV 訂閱方法
- settings: 新增系統設定 API (site_title/version/timezone/SSO/Keycloak)
- models/result: 新增 nc_mail_result, nc_mail_done_at 欄位
- alembic: 遷移 002(system_settings) 003(keycloak_admin) 004(nc_mail_result)

Frontend (Admin Portal):
- 新增完整管理後台 (index/tenants/accounts/servers/schedules/logs/settings/system-status)
- api.js: Keycloak JS Adapter SSO 整合 (PKCE/S256, fallback KC JS 來源, 自動 token 更新)
- index.html: Promise.allSettled 取代 Promise.all，防止單一 API 失敗影響整頁
- 所有頁面加入 try/catch + toast 錯誤處理
- 新增品牌 LOGO 與 favicon

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

backend/app/services/scheduler/watchdog.py

@@ -4,6 +4,7 @@ Watchdog: APScheduler BackgroundScheduler，每 3 分鐘掃描 schedules 表。
 """
 import logging
 from datetime import datetime
+from app.core.utils import now_tw
 from apscheduler.schedulers.background import BackgroundScheduler
 from croniter import croniter
 from sqlalchemy import update
@@ -24,7 +25,7 @@ def _watchdog_tick():
             db.query(Schedule)
             .filter(
                 Schedule.status == "Waiting",
-                Schedule.next_run_at <= datetime.utcnow(),
+                Schedule.next_run_at <= now_tw(),
             )
             .all()
         )
@@ -44,7 +45,7 @@ def _watchdog_tick():
             log = ScheduleLog(
                 schedule_id=schedule.id,
                 schedule_name=schedule.name,
-                started_at=datetime.utcnow(),
+                started_at=now_tw(),
                 status="running",
             )
             db.add(log)
@@ -60,12 +61,12 @@ def _watchdog_tick():
                 final_status = "error"
 
             # Update log
-            log.ended_at = datetime.utcnow()
+            log.ended_at = now_tw()
             log.status = final_status
 
-            # Recalculate next_run_at
+            # Recalculate next_run_at (5-field cron: 分 時 日 月 週)
             try:
-                cron = croniter(schedule.cron_timer, datetime.utcnow())
+                cron = croniter(schedule.cron_timer, now_tw())
                 next_run = cron.get_next(datetime)
             except Exception:
                 next_run = None
@@ -76,7 +77,7 @@ def _watchdog_tick():
                 .where(Schedule.id == schedule.id)
                 .values(
                     status="Waiting",
-                    last_run_at=datetime.utcnow(),
+                    last_run_at=now_tw(),
                     next_run_at=next_run,
                     last_status=final_status,
                 )