Require additional user confirmation for making repo private (#36959)

To align with how GitHub requires additional explicit user interaction
to make a repo private, including informing them of implications on what
happens if they do.

---------

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

tests/integration/repo_visibility_test.go

@@ -0,0 +1,59 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"net/http"
+	"testing"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/modules/test"
+	"code.gitea.io/gitea/tests"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRepositoryVisibilityChange(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+	session := loginUser(t, "user2")
+
+	t.Run("MakePrivateRequiresCorrectName", func(t *testing.T) {
+		// Wrong name should be rejected with a JSON error
+		req := NewRequestWithValues(t, "POST", "/user2/repo1/settings", map[string]string{
+			"action":            "visibility",
+			"private":           "true",
+			"confirm_repo_name": "wrong-name",
+		})
+		resp := session.MakeRequest(t, req, http.StatusBadRequest)
+		assert.NotEmpty(t, test.ParseJSONError(resp.Body.Bytes()).ErrorMessage)
+
+		repo1 := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+		assert.False(t, repo1.IsPrivate)
+
+		// Correct full name (owner/repo) should succeed with a JSON redirect
+		req = NewRequestWithValues(t, "POST", "/user2/repo1/settings", map[string]string{
+			"action":            "visibility",
+			"private":           "true",
+			"confirm_repo_name": "user2/repo1",
+		})
+		resp = session.MakeRequest(t, req, http.StatusOK)
+		assert.NotEmpty(t, test.ParseJSONRedirect(resp.Body.Bytes()).Redirect)
+
+		repo1 = unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+		assert.True(t, repo1.IsPrivate)
+	})
+
+	t.Run("MakePublicDoesNotRequireName", func(t *testing.T) {
+		req := NewRequestWithValues(t, "POST", "/user2/repo2/settings", map[string]string{
+			"action":  "visibility",
+			"private": "false",
+		})
+		resp := session.MakeRequest(t, req, http.StatusOK)
+		assert.NotEmpty(t, test.ParseJSONRedirect(resp.Body.Bytes()).Redirect)
+
+		repo2 := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 2})
+		assert.False(t, repo2.IsPrivate)
+	})
+}