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/seed.py

@@ -1,9 +1,11 @@
-"""Initial data seed: schedules + servers"""
+"""Initial data seed: schedules + servers + system settings"""
 from datetime import datetime
+from app.core.utils import now_tw, configure_timezone
 from croniter import croniter
 from sqlalchemy.orm import Session
 from app.models.schedule import Schedule
 from app.models.server import Server
+from app.models.settings import SystemSettings
 
 
 INITIAL_SCHEDULES = [
@@ -26,7 +28,7 @@ INITIAL_SERVERS = [
 
 def _calc_next_run(cron_timer: str) -> datetime:
     # croniter: six-field cron (sec min hour day month weekday)
-    cron = croniter(cron_timer, datetime.utcnow())
+    cron = croniter(cron_timer, now_tw())
     return cron.get_next(datetime)
 
 
@@ -46,4 +48,13 @@ def seed_initial_data(db: Session) -> None:
         if not db.get(Server, sv["id"]):
             db.add(Server(**sv))
 
+    # Seed default system settings (id=1)
+    if not db.get(SystemSettings, 1):
+        db.add(SystemSettings(id=1))
+
     db.commit()
+
+    # Apply timezone from settings
+    s = db.get(SystemSettings, 1)
+    if s:
+        configure_timezone(s.timezone)