api: use webui.ServeSPA in NotFound handler instead of buggy inline logic

internal/api/router.go

@@ -81,17 +81,7 @@ func NewServer(cfg *config.Config, db *sql.DB, engine *syncengine.Engine) *Serve
 	}))
 
 	r.NotFound(func(w http.ResponseWriter, r *http.Request) {
-		if _, ok := webui.DistFS.Open("dist" + r.URL.Path); ok == nil {
-			http.FileServer(http.FS(webui.DistFS)).ServeHTTP(w, r)
-			return
-		}
-		data, err := webui.DistFS.ReadFile("dist/index.html")
-		if err != nil {
-			http.Error(w, "not found", http.StatusNotFound)
-			return
-		}
-		w.Header().Set("Content-Type", "text/html")
-		w.Write(data)
+		webui.ServeSPA().ServeHTTP(w, r)
 	})
 
 	return s