fix(1panel): grant nexus@% for Docker MySQL 1045 on install

Add fix-1panel-mysql-grant.sh and clearer install wizard errors when
1Panel MySQL only allows nexus@localhost.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/changelog/2026-06-06-1panel-mysql-1045-grant.md

@@ -0,0 +1,27 @@
+# 2026-06-06 — 1Panel MySQL 1045 授权修复
+
+## 摘要
+
+安装向导步骤 3 报 `Access denied for user 'nexus'@'172.18.x.x'`：1Panel 常见仅 `nexus@localhost`，Docker 网段连接被拒。新增 `fix-1panel-mysql-grant.sh` 与安装 API 明确错误提示。
+
+## 动机
+
+验收脚本已通过但 init-db 1045；需在仓库内提供可重复修复路径，避免手工 SQL 易错。
+
+## 涉及文件
+
+- `deploy/fix-1panel-mysql-grant.sh` — 创建/授权 `nexus@'%'`
+- `server/api/install.py` — 1045 友好错误与 connection-check
+- `deploy/README-1panel.md` — 1045 排障节
+
+## 验证
+
+```bash
+MYSQL_ROOT_PASSWORD='...' NEXUS_DB_PASSWORD='...' bash deploy/fix-1panel-mysql-grant.sh
+# 安装向导步骤 3 初始化成功
+bash deploy/sync-install-wizard-to-container.sh   # 同步 install.py 到运行中容器
+```
+
+## 迁移 / 重启
+
+无 DB 迁移。`install.py` 变更需 `sync-install-wizard-to-container.sh` 或 `nx update --no-cache`。