feat(managed-ne): add bulk import template download with device_type reference sheet

Expose GET /v1/managed-ne/import/template and a workbench button to download xlsx/csv templates listing supported Netmiko device types.

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

web/src/i18n/en.ts

@@ -102,6 +102,7 @@ const en = {
       "NETX_CREDENTIAL_SECRET_KEY is not set. Configure a Fernet key in .env and restart the API to store passwords.",
     add: "Add NE",
     importBtn: "Import",
+    downloadTemplate: "Download template",
     importing: "Importing…",
     edit: "Edit",
     delete: "Delete",

web/src/i18n/zh.ts

@@ -101,6 +101,7 @@ const zh = {
     credsNotConfigured: "未配置 NETX_CREDENTIAL_SECRET_KEY，无法保存密码。请在 .env 中设置 Fernet 密钥后重启 API。",
     add: "新增网元",
     importBtn: "批量导入",
+    downloadTemplate: "下载导入模板",
     importing: "导入中…",
     edit: "编辑",
     delete: "删除",