v2.1: 新增通知提醒功能和安全增强

功能:
- 通知提醒系统: 还款日提醒、逾期提醒、系统消息横幅、登录时通知
- 通知中心UI: 铃铛图标 + 下拉列表 + 未读徽章
- 定时任务: APScheduler 每小时检查即将到期的还款
- 邮件通知: SMTP 发送还款提醒和安全警告
- 异常登录通知: 3/5/10次失败触发网页和邮件通知

安全:
- 登录安全告警: 异常登录次数达到阈值时发送通知
- 密码重置链接: 一次性使用, 5分钟有效期
- 登录频率限制: IP级和账户级限制

技术:
- 后端: FastAPI + SQLAlchemy + PostgreSQL
- 前端: 纯 HTML/CSS/JS
- 部署: Docker Compose (新增 build 配置)

backend/app/services/scheduler.py

@@ -0,0 +1,105 @@
+from apscheduler.schedulers.asyncio import AsyncIOScheduler
+from sqlalchemy import select, and_
+from datetime import datetime, timedelta
+from app.core.database import async_session
+from app.core.config import get_settings
+from app.models.models import (
+    Debt, Notification, NotificationType, User, DebtStatus
+)
+from app.services.notification_service import create_notification
+from app.services.email_service import send_email, build_repayment_reminder_html
+
+settings = get_settings()
+scheduler = AsyncIOScheduler()
+
+
+async def check_upcoming_repayments():
+    async with async_session() as db:
+        now = datetime.utcnow()
+        reminder_days = settings.REMINDER_DAYS_BEFORE
+        check_window = now + timedelta(days=reminder_days)
+
+        result = await db.execute(
+            select(Debt).where(
+                and_(
+                    Debt.status == DebtStatus.ACTIVE.value,
+                    Debt.schedule_data.isnot(None),
+                )
+            )
+        )
+        debts = result.scalars().all()
+
+        for debt in debts:
+            schedule = debt.schedule_data or []
+            paid_periods = debt.paid_periods or []
+            user_result = await db.execute(select(User).where(User.id == debt.user_id))
+            user = user_result.scalar_one_or_none()
+            if not user:
+                continue
+
+            for item in schedule:
+                p = item.get("p")
+                if p in paid_periods:
+                    continue
+
+                try:
+                    due_date = datetime.strptime(item["date"], "%Y-%m-%d")
+                except (ValueError, KeyError):
+                    continue
+
+                if due_date > check_window:
+                    continue
+
+                is_overdue = due_date < now
+                amount_yuan = item.get("pay", 0)
+                days_left = (due_date - now).days
+
+                if is_overdue:
+                    ntype = NotificationType.REPAYMENT_OVERDUE.value
+                    title = f"逾期提醒：{debt.creditor_name} 第{p}期还款已逾期"
+                    msg = f"您在 {debt.creditor_name} 的第{p}期 ¥{amount_yuan:,.2f} 还款已于 {item['date']} 逾期，请尽快处理。"
+                else:
+                    ntype = NotificationType.REPAYMENT_DUE.value
+                    title = f"还款提醒：{debt.creditor_name} 第{p}期将在 {days_left} 天后到期"
+                    msg = f"您在 {debt.creditor_name} 的第{p}期 ¥{amount_yuan:,.2f} 将于 {item['date']} 到期，请按时还款。"
+
+                existing = await db.execute(
+                    select(Notification).where(
+                        and_(
+                            Notification.user_id == user.id,
+                            Notification.related_debt_id == debt.id,
+                            Notification.title == title,
+                        )
+                    )
+                )
+                if existing.scalar_one_or_none():
+                    continue
+
+                await create_notification(
+                    db, user.id, title, msg, ntype,
+                    related_debt_id=debt.id,
+                )
+
+                if user.email and "@" in user.email:
+                    html = build_repayment_reminder_html(
+                        user.nickname or user.email,
+                        debt.creditor_name,
+                        amount_yuan,
+                        item["date"],
+                        days_left,
+                        is_overdue,
+                    )
+                    await send_email(user.email, title, html)
+
+        await db.commit()
+
+
+def start_scheduler():
+    scheduler.add_job(
+        check_upcoming_repayments,
+        "interval",
+        minutes=settings.NOTIFICATION_CHECK_INTERVAL_MINUTES,
+        id="repayment_check",
+        replace_existing=True,
+    )
+    scheduler.start()