Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

ui/entry_enclosure_save_position.go

@@ -1,53 +0,0 @@
-// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
-// SPDX-License-Identifier: Apache-2.0
-
-package ui // import "miniflux.app/v2/ui"
-
-import (
-	json2 "encoding/json"
-	"io"
-	"net/http"
-
-	"miniflux.app/v2/http/request"
-	"miniflux.app/v2/http/response/json"
-)
-
-func (h *handler) saveEnclosureProgression(w http.ResponseWriter, r *http.Request) {
-	enclosureID := request.RouteInt64Param(r, "enclosureID")
-	enclosure, err := h.store.GetEnclosure(enclosureID)
-	if err != nil {
-		json.ServerError(w, r, err)
-		return
-	}
-
-	if enclosure == nil {
-		json.NotFound(w, r)
-		return
-	}
-
-	type enclosurePositionSaveRequest struct {
-		Progression int64 `json:"progression"`
-	}
-
-	var postData enclosurePositionSaveRequest
-	body, err := io.ReadAll(r.Body)
-	if err != nil {
-		json.ServerError(w, r, err)
-		return
-	}
-
-	json2.Unmarshal(body, &postData)
-	if err != nil {
-		json.ServerError(w, r, err)
-		return
-	}
-	enclosure.MediaProgression = postData.Progression
-
-	err = h.store.UpdateEnclosure(enclosure)
-	if err != nil {
-		json.ServerError(w, r, err)
-		return
-	}
-
-	json.Created(w, r, map[string]string{"message": "saved"})
-}