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/servers.py

@@ -0,0 +1,104 @@
+from typing import List, Optional
+from datetime import datetime, timedelta
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy import func, case
+from sqlalchemy.orm import Session
+
+from app.core.database import get_db
+from app.models.server import Server, ServerStatusLog
+from app.schemas.server import ServerCreate, ServerUpdate, ServerResponse, ServerAvailability
+
+router = APIRouter(prefix="/servers", tags=["servers"])
+
+
+def _calc_availability(db: Session, server_id: int, days: int) -> Optional[float]:
+    since = datetime.utcnow() - timedelta(days=days)
+    row = (
+        db.query(
+            func.count().label("total"),
+            func.sum(case((ServerStatusLog.result == True, 1), else_=0)).label("ok"),
+        )
+        .filter(ServerStatusLog.server_id == server_id, ServerStatusLog.recorded_at >= since)
+        .first()
+    )
+    if not row or not row.total:
+        return None
+    return round(row.ok * 100.0 / row.total, 2)
+
+
+def _get_last_status(db: Session, server_id: int):
+    return (
+        db.query(ServerStatusLog)
+        .filter(ServerStatusLog.server_id == server_id)
+        .order_by(ServerStatusLog.recorded_at.desc(), ServerStatusLog.id.desc())
+        .first()
+    )
+
+
+@router.get("", response_model=List[ServerResponse])
+def list_servers(db: Session = Depends(get_db)):
+    servers = db.query(Server).order_by(Server.sort_order).all()
+    result = []
+    for s in servers:
+        resp = ServerResponse.model_validate(s)
+        last = _get_last_status(db, s.id)
+        if last:
+            resp.last_result = last.result
+            resp.last_response_time = last.response_time
+        resp.availability = ServerAvailability(
+            availability_30d=_calc_availability(db, s.id, 30),
+            availability_90d=_calc_availability(db, s.id, 90),
+            availability_365d=_calc_availability(db, s.id, 365),
+        )
+        result.append(resp)
+    return result
+
+
+@router.post("", response_model=ServerResponse, status_code=201)
+def create_server(payload: ServerCreate, db: Session = Depends(get_db)):
+    if db.query(Server).filter(Server.ip_address == payload.ip_address).first():
+        raise HTTPException(status_code=409, detail="IP address already exists")
+    server = Server(**payload.model_dump())
+    db.add(server)
+    db.commit()
+    db.refresh(server)
+    return ServerResponse.model_validate(server)
+
+
+@router.get("/{server_id}", response_model=ServerResponse)
+def get_server(server_id: int, db: Session = Depends(get_db)):
+    server = db.get(Server, server_id)
+    if not server:
+        raise HTTPException(status_code=404, detail="Server not found")
+    resp = ServerResponse.model_validate(server)
+    last = _get_last_status(db, server_id)
+    if last:
+        resp.last_result = last.result
+        resp.last_response_time = last.response_time
+    resp.availability = ServerAvailability(
+        availability_30d=_calc_availability(db, server_id, 30),
+        availability_90d=_calc_availability(db, server_id, 90),
+        availability_365d=_calc_availability(db, server_id, 365),
+    )
+    return resp
+
+
+@router.put("/{server_id}", response_model=ServerResponse)
+def update_server(server_id: int, payload: ServerUpdate, db: Session = Depends(get_db)):
+    server = db.get(Server, server_id)
+    if not server:
+        raise HTTPException(status_code=404, detail="Server not found")
+    for field, value in payload.model_dump(exclude_none=True).items():
+        setattr(server, field, value)
+    db.commit()
+    db.refresh(server)
+    return ServerResponse.model_validate(server)
+
+
+@router.delete("/{server_id}", status_code=204)
+def delete_server(server_id: int, db: Session = Depends(get_db)):
+    server = db.get(Server, server_id)
+    if not server:
+        raise HTTPException(status_code=404, detail="Server not found")
+    db.delete(server)
+    db.commit()