feat: add read-only mode to API and UI, disable write actions

internal/ffmpeg/api.go

@@ -4,6 +4,7 @@ import (
 	"net/http"
 	"strings"
 
+	"github.com/AlexxIT/go2rtc/internal/api"
 	"github.com/AlexxIT/go2rtc/internal/streams"
 )
 
@@ -12,6 +13,10 @@ func apiFFmpeg(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "", http.StatusMethodNotAllowed)
 		return
 	}
+	if api.IsReadOnly() {
+		api.ReadOnlyError(w)
+		return
+	}
 
 	query := r.URL.Query()
 	dst := query.Get("dst")