feat: add safe backup management and theme preferences

Add snapshot usage and protected cleanup, preserve unsaved profile edits, avoid holding SQL connections during snapshot deletion, and fix download filenames. Include regression tests and API documentation.

internal/api/config.go

@@ -23,6 +23,10 @@ var backupIDPattern = regexp.MustCompile("^[a-f0-9]{32}$")
 var configBodySlots = make(chan struct{}, 4)
 
 func (a *API) config(w http.ResponseWriter, r *http.Request, i store.Instance, action string) {
+	if action == "snapshots" || (action == "backups" && r.Method == http.MethodDelete) {
+		a.backupManagement(w, r, i, action)
+		return
+	}
 	controller := http.NewResponseController(w)
 	if r.Method != http.MethodGet || action != "backups" || r.URL.Query().Get("download") == "" {
 		var flush func()