refactor: 数据源菜单合一+布局优化

- 4个数据源菜单(MySQL/PG/Redis/Mongo)合并为1个「数据源」
- InstancePage 改为统一入口，顶部Tab切换类型过滤
- 添加数据源改为弹框Modal（默认MySQL）
- 去掉左下角用户区，退出登录移到右上角header
- 侧边栏收窄220px，整体布局更紧凑
- 后端202 tests passing
- 前端构建零错误

backend/app/api/v1/endpoints/backup.py

@@ -0,0 +1,62 @@
+"""Backup management API."""
+from typing import Optional, List
+
+from fastapi import APIRouter, Depends, HTTPException, Query
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.database import get_db
+from app.core.security import require_role
+from app.models.user import User
+from app.models.backup import Backup
+from app.schemas.backup import BackupCreate, BackupResponse
+
+router = APIRouter(prefix="/backups", tags=["备份管理"])
+
+
+@router.get("", response_model=List[BackupResponse])
+async def list_backups(
+    instance_id: Optional[int] = Query(None),
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(require_role("admin", "dba")),
+):
+    stmt = select(Backup).order_by(Backup.id.desc())
+    if instance_id:
+        stmt = stmt.where(Backup.instance_id == instance_id)
+    result = await db.execute(stmt)
+    backups = result.scalars().all()
+    return backups
+
+
+@router.post("", response_model=BackupResponse, status_code=201)
+async def create_backup(
+    data: BackupCreate,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(require_role("admin", "dba")),
+):
+    backup = Backup(
+        title=data.title,
+        instance_id=data.instance_id,
+        database=data.database,
+        filename=data.database + "_" + str(data.instance_id) + ".sql",
+        status="pending",
+        created_by=current_user.id,
+        remark=data.remark,
+    )
+    db.add(backup)
+    await db.commit()
+    await db.refresh(backup)
+    return backup
+
+
+@router.get("/{backup_id}", response_model=BackupResponse)
+async def get_backup(
+    backup_id: int,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(require_role("admin", "dba")),
+):
+    result = await db.execute(select(Backup).where(Backup.id == backup_id))
+    backup = result.scalar_one_or_none()
+    if not backup:
+        raise HTTPException(status_code=404, detail="备份记录不存在")
+    return backup