Read issue/PR description from stdin or a file (#1096)

Closes #1095.

`tea issues create` and `tea pulls create` now resolve the description in the same way as comments: when stdin is piped and neither `--description` nor `--description-file` is given, the body is read from stdin. Both create and edit commands also accept:

```text
--description-file <path>   # '-' reads stdin
```

This avoids the PowerShell 5.1 argument mangling and ANSI code page issues described in #1095.

## Changes

- Add `--description-file` to `issues create`, `issues edit`, `pulls create`, and `pulls edit`.
- Create commands fall back to piped stdin when no description flag is set.
- Add unit tests for the new body resolution.

---------

Co-authored-by: bircni <bircni@icloud.com>
Reviewed-on: https://gitea.com/gitea/tea/pulls/1096
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

cmd/flags/body_test.go

@@ -0,0 +1,161 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package flags
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestResolveCreateBody(t *testing.T) {
+	file := filepath.Join(t.TempDir(), "body.md")
+	require.NoError(t, os.WriteFile(file, []byte("from file"), 0o600))
+
+	tests := []struct {
+		name               string
+		description        string
+		descriptionFile    string
+		descriptionFileSet bool
+		stdinPiped         bool
+		stdin              string
+		want               string
+	}{
+		{
+			name:        "description flag",
+			description: "from -d",
+			want:        "from -d",
+		},
+		{
+			name:               "description file",
+			descriptionFile:    file,
+			descriptionFileSet: true,
+			want:               "from file",
+		},
+		{
+			name:               "description file wins over description",
+			description:        "from -d",
+			descriptionFile:    file,
+			descriptionFileSet: true,
+			want:               "from file",
+		},
+		{
+			name:               "dash reads stdin",
+			descriptionFile:    "-",
+			descriptionFileSet: true,
+			stdin:              "from stdin",
+			want:               "from stdin",
+		},
+		{
+			name:        "description wins over piped stdin",
+			description: "from -d",
+			stdinPiped:  true,
+			stdin:       "from stdin",
+			want:        "from -d",
+		},
+		{
+			name:       "piped stdin",
+			stdinPiped: true,
+			stdin:      "from stdin",
+			want:       "from stdin",
+		},
+		{
+			name:        "empty description falls back to piped stdin",
+			description: "",
+			stdinPiped:  true,
+			stdin:       "from stdin",
+			want:        "from stdin",
+		},
+		{
+			name: "empty when no source provided",
+			want: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := resolveCreateBody(tt.description, tt.descriptionFile, tt.descriptionFileSet, tt.stdinPiped, strings.NewReader(tt.stdin))
+			require.NoError(t, err)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}
+
+func TestResolveEditBody(t *testing.T) {
+	file := filepath.Join(t.TempDir(), "body.md")
+	require.NoError(t, os.WriteFile(file, []byte("from file"), 0o600))
+
+	tests := []struct {
+		name               string
+		description        string
+		descriptionSet     bool
+		descriptionFile    string
+		descriptionFileSet bool
+		stdin              string
+		wantBody           string
+		wantSet            bool
+	}{
+		{
+			name: "no description flag",
+		},
+		{
+			name:           "description flag",
+			description:    "from -d",
+			descriptionSet: true,
+			wantBody:       "from -d",
+			wantSet:        true,
+		},
+		{
+			name:           "empty description clears body",
+			descriptionSet: true,
+			wantSet:        true,
+		},
+		{
+			name:               "description file",
+			descriptionFile:    file,
+			descriptionFileSet: true,
+			wantBody:           "from file",
+			wantSet:            true,
+		},
+		{
+			name:               "description file wins over description",
+			description:        "from -d",
+			descriptionSet:     true,
+			descriptionFile:    file,
+			descriptionFileSet: true,
+			wantBody:           "from file",
+			wantSet:            true,
+		},
+		{
+			name:               "dash reads stdin",
+			descriptionFile:    "-",
+			descriptionFileSet: true,
+			stdin:              "from stdin",
+			wantBody:           "from stdin",
+			wantSet:            true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := resolveEditBody(tt.description, tt.descriptionSet, tt.descriptionFile, tt.descriptionFileSet, strings.NewReader(tt.stdin))
+			require.NoError(t, err)
+			if !tt.wantSet {
+				assert.Nil(t, got)
+				return
+			}
+			require.NotNil(t, got)
+			assert.Equal(t, tt.wantBody, *got)
+		})
+	}
+}
+
+func TestResolveDescriptionSourceError(t *testing.T) {
+	_, err := resolveCreateBody("", filepath.Join(t.TempDir(), "missing.md"), true, false, strings.NewReader(""))
+	require.ErrorContains(t, err, "could not read description file")
+}