revert: tea 1.0 rewrite (#1122–#1126) (#1146)

Reverts #1126, #1125, #1124, #1123 and #1122.

`go.mod` keeps the Go 1.26 line with toolchain `go1.26.9` (instead of the original `go1.26.6`) so the security fix from #1131 isn't lost.

reopens #69
reopens #141
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Reviewed-on: https://gitea.com/gitea/tea/pulls/1146
Reviewed-by: TheFox0x7 <95654+thefox0x7@noreply.gitea.com>

modules/git/cli_backend_test.go

@@ -0,0 +1,40 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestOpenClassifiesLocalizedNotRepoError(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("test uses a POSIX shell script as fake git")
+	}
+
+	fakeGitDir := t.TempDir()
+	fakeGit := filepath.Join(fakeGitDir, "git")
+	script := `#!/bin/sh
+locale="${LC_ALL:-${LANG:-C}}"
+if [ "$locale" = "C" ]; then
+	echo "fatal: not a git repository (or any of the parent directories): .git" >&2
+else
+	echo "fatal: Kein Git-Repository (oder irgendein Elternverzeichnis bis zum Einhangepunkt /)" >&2
+fi
+exit 128
+`
+	require.NoError(t, os.WriteFile(fakeGit, []byte(script), 0o755))
+
+	t.Setenv("PATH", fakeGitDir+string(os.PathListSeparator)+os.Getenv("PATH"))
+	t.Setenv("LC_ALL", "de_DE.UTF-8")
+	t.Setenv("LANG", "de_DE.UTF-8")
+	t.Setenv("LANGUAGE", "de_DE:de")
+
+	_, err := (cliBackend{}).Open(t.TempDir())
+	require.ErrorIs(t, err, ErrRepositoryNotExists)
+}