add backup API endoint docs

mkdocs/docs/api/backup.md

@@ -0,0 +1,38 @@
+# Backup
+
+Index [snapshots](snapshot.md) are a more reliable way than zip file backup as described here.
+
+## Backup List
+**GET** `/api/backup/`  
+Return a list of available backup files with metadata.
+
+**POST** `/api/backup/`  
+Start a backup task now. This will return immediately, triggering an async task in the background. The message will contain a `task_id` key that can be monitored separately.
+
+Example return message:
+```json
+{
+	"message": "backup task started",
+	"task_id": "f22f6981-35bb-4b7c-bd91-80a57d960b52"
+}
+```
+
+## Backup Item
+**GET** `/api/backup/<filename>/`  
+Return metadata of a single backup file.
+
+**POST** `/api/backup/<filename>/`  
+Start a backup restore task now. This will return immediately, triggering an async task in the background. The message will contain a `task_id` key that can be monitored separately.
+
+Example return message:
+
+```json
+{
+	"message": "backup restore task started",
+	"filename": "ta_backup-20231101-auto.zip",
+	"task_id": "4fc2afdf-4045-4288-a33c-e3267a9efb5a"
+}
+```
+
+**DELETE** `/api/backup/<filename>/`  
+Delete backup file from the filesystem.

mkdocs/mkdocs.yml

@@ -36,6 +36,7 @@ nav:
         - 'Playlist': 'api/playlist.md'
         - 'Download': 'api/download.md'
         - 'Snapshot': 'api/snapshot.md'
+        - 'Backup': 'api/backup.md'
         - 'Task': 'api/task.md'
         - 'Stats': 'api/stats.md'
         - 'Additional': 'api/additional.md'