Fix README symlink resolution in subdirectories like .github (#36775)

Fixes #36774.

---------

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

routers/web/repo/view_readme.go

@@ -102,7 +102,7 @@ func findReadmeFileInEntries(ctx *context.Context, parentDir string, entries []*
 				return "", nil, err
 			}
 
-			subfolder, readmeFile, err := findReadmeFileInEntries(ctx, parentDir, childEntries, false)
+			subfolder, readmeFile, err := findReadmeFileInEntries(ctx, path.Join(parentDir, subTreeEntry.Name()), childEntries, false)
 			if err != nil && !git.IsErrNotExist(err) {
 				return "", nil, err
 			}

routers/web/repo/view_readme_test.go

@@ -0,0 +1,70 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repo
+
+import (
+	"fmt"
+	"path"
+	"testing"
+
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/git/gitcmd"
+	"code.gitea.io/gitea/services/contexttest"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFindReadmeFileInEntriesWithSymlinkInSubfolder(t *testing.T) {
+	for _, subdir := range []string{".github", ".gitea", "docs"} {
+		t.Run(subdir, func(t *testing.T) {
+			repoPath := t.TempDir()
+			stdin := fmt.Sprintf(`commit refs/heads/master
+author Test <test@example.com> 1700000000 +0000
+committer Test <test@example.com> 1700000000 +0000
+data <<EOT
+initial
+EOT
+M 100644 inline target.md
+data <<EOT
+target-content
+EOT
+M 120000 inline %s/README.md
+data 12
+../target.md
+`, subdir)
+
+			var err error
+			err = gitcmd.NewCommand("init", "--bare", ".").WithDir(repoPath).RunWithStderr(t.Context())
+			require.NoError(t, err)
+			err = gitcmd.NewCommand("fast-import").WithDir(repoPath).WithStdinBytes([]byte(stdin)).RunWithStderr(t.Context())
+			require.NoError(t, err)
+
+			gitRepo, err := git.OpenRepository(t.Context(), repoPath)
+			require.NoError(t, err)
+			defer gitRepo.Close()
+
+			commit, err := gitRepo.GetBranchCommit("master")
+			require.NoError(t, err)
+
+			entries, err := commit.ListEntries()
+			require.NoError(t, err)
+
+			ctx, _ := contexttest.MockContext(t, "/")
+			ctx.Repo.Commit = commit
+			foundDir, foundReadme, err := findReadmeFileInEntries(ctx, "", entries, true)
+			require.NoError(t, err)
+			require.NotNil(t, foundReadme)
+
+			assert.Equal(t, subdir, foundDir)
+			assert.Equal(t, "README.md", foundReadme.Name())
+			assert.True(t, foundReadme.IsLink())
+
+			// Verify that it can follow the link
+			res, err := git.EntryFollowLinks(commit, path.Join(foundDir, foundReadme.Name()), foundReadme)
+			require.NoError(t, err)
+			assert.Equal(t, "target.md", res.TargetFullPath)
+		})
+	}
+}