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/api/v1/accounts.py

@@ -0,0 +1,118 @@
+from typing import List, Optional
+from fastapi import APIRouter, Depends, HTTPException, Query
+from sqlalchemy.orm import Session
+
+from app.core.database import get_db
+from app.models.account import Account
+from app.models.tenant import Tenant
+from app.models.result import AccountScheduleResult
+from app.schemas.account import AccountCreate, AccountUpdate, AccountResponse, AccountStatusLight
+
+router = APIRouter(prefix="/accounts", tags=["accounts"])
+
+
+def _next_seq_no(db: Session, tenant_id: int) -> int:
+    max_seq = db.query(Account.seq_no).filter(Account.tenant_id == tenant_id).order_by(Account.seq_no.desc()).first()
+    return (max_seq[0] + 1) if max_seq else 1
+
+
+def _build_account_code(prefix: str, seq_no: int) -> str:
+    return f"{prefix}{str(seq_no).zfill(4)}"
+
+
+def _get_lights(db: Session, account_id: int) -> Optional[AccountStatusLight]:
+    result = (
+        db.query(AccountScheduleResult)
+        .filter(AccountScheduleResult.account_id == account_id)
+        .order_by(AccountScheduleResult.recorded_at.desc())
+        .first()
+    )
+    if not result:
+        return None
+    return AccountStatusLight(
+        sso_result=result.sso_result,
+        mailbox_result=result.mailbox_result,
+        nc_result=result.nc_result,
+        quota_usage=result.quota_usage,
+    )
+
+
+@router.get("", response_model=List[AccountResponse])
+def list_accounts(
+    tenant_id: Optional[int] = Query(None),
+    is_active: Optional[bool] = Query(None),
+    db: Session = Depends(get_db),
+):
+    q = db.query(Account)
+    if tenant_id is not None:
+        q = q.filter(Account.tenant_id == tenant_id)
+    if is_active is not None:
+        q = q.filter(Account.is_active == is_active)
+    accounts = q.order_by(Account.id).all()
+    result = []
+    for a in accounts:
+        resp = AccountResponse.model_validate(a)
+        resp.tenant_name = a.tenant.name if a.tenant else None
+        resp.lights = _get_lights(db, a.id)
+        result.append(resp)
+    return result
+
+
+@router.post("", response_model=AccountResponse, status_code=201)
+def create_account(payload: AccountCreate, db: Session = Depends(get_db)):
+    tenant = db.get(Tenant, payload.tenant_id)
+    if not tenant:
+        raise HTTPException(status_code=404, detail="Tenant not found")
+
+    seq_no = _next_seq_no(db, payload.tenant_id)
+    account_code = _build_account_code(tenant.prefix, seq_no)
+    email = f"{payload.sso_account}@{tenant.domain}"
+
+    account = Account(
+        **payload.model_dump(),
+        seq_no=seq_no,
+        account_code=account_code,
+        email=email,
+    )
+    db.add(account)
+    db.commit()
+    db.refresh(account)
+    resp = AccountResponse.model_validate(account)
+    resp.tenant_name = tenant.name
+    resp.lights = None
+    return resp
+
+
+@router.get("/{account_id}", response_model=AccountResponse)
+def get_account(account_id: int, db: Session = Depends(get_db)):
+    account = db.get(Account, account_id)
+    if not account:
+        raise HTTPException(status_code=404, detail="Account not found")
+    resp = AccountResponse.model_validate(account)
+    resp.tenant_name = account.tenant.name if account.tenant else None
+    resp.lights = _get_lights(db, account_id)
+    return resp
+
+
+@router.put("/{account_id}", response_model=AccountResponse)
+def update_account(account_id: int, payload: AccountUpdate, db: Session = Depends(get_db)):
+    account = db.get(Account, account_id)
+    if not account:
+        raise HTTPException(status_code=404, detail="Account not found")
+    for field, value in payload.model_dump(exclude_none=True).items():
+        setattr(account, field, value)
+    db.commit()
+    db.refresh(account)
+    resp = AccountResponse.model_validate(account)
+    resp.tenant_name = account.tenant.name if account.tenant else None
+    resp.lights = _get_lights(db, account_id)
+    return resp
+
+
+@router.delete("/{account_id}", status_code=204)
+def delete_account(account_id: int, db: Session = Depends(get_db)):
+    account = db.get(Account, account_id)
+    if not account:
+        raise HTTPException(status_code=404, detail="Account not found")
+    db.delete(account)
+    db.commit()