Fix javascript error when an anonymous user visiting migration page (#32144)

This PR fixes javascript errors when an anonymous user visits the
migration page.
It also makes task view checking more restrictive.

The router moved from `/user/task/{id}/status` to
`/username/reponame/-/migrate/status` because it's a migrate status.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/user/task.go

@@ -1,53 +0,0 @@
-// Copyright 2020 The Gitea Authors. All rights reserved.
-// SPDX-License-Identifier: MIT
-
-package user
-
-import (
-	"net/http"
-	"strconv"
-
-	admin_model "code.gitea.io/gitea/models/admin"
-	"code.gitea.io/gitea/modules/json"
-	"code.gitea.io/gitea/services/context"
-)
-
-// TaskStatus returns task's status
-func TaskStatus(ctx *context.Context) {
-	task, opts, err := admin_model.GetMigratingTaskByID(ctx, ctx.PathParamInt64("task"), ctx.Doer.ID)
-	if err != nil {
-		if admin_model.IsErrTaskDoesNotExist(err) {
-			ctx.JSON(http.StatusNotFound, map[string]any{
-				"error": "task `" + strconv.FormatInt(ctx.PathParamInt64("task"), 10) + "` does not exist",
-			})
-			return
-		}
-		ctx.JSON(http.StatusInternalServerError, map[string]any{
-			"err": err,
-		})
-		return
-	}
-
-	message := task.Message
-
-	if task.Message != "" && task.Message[0] == '{' {
-		// assume message is actually a translatable string
-		var translatableMessage admin_model.TranslatableMessage
-		if err := json.Unmarshal([]byte(message), &translatableMessage); err != nil {
-			translatableMessage = admin_model.TranslatableMessage{
-				Format: "migrate.migrating_failed.error",
-				Args:   []any{task.Message},
-			}
-		}
-		message = ctx.Locale.TrString(translatableMessage.Format, translatableMessage.Args...)
-	}
-
-	ctx.JSON(http.StatusOK, map[string]any{
-		"status":    task.Status,
-		"message":   message,
-		"repo-id":   task.RepoID,
-		"repo-name": opts.RepoName,
-		"start":     task.StartTime,
-		"end":       task.EndTime,
-	})
-}