feat(comments): accept -d/--description for comment body (#1043)

Closes #1042.

### What

`tea issue create`, `tea issue edit` and `tea pr create` all take the body via
`-d` / `--description`, but `tea comments add` and `tea comments edit` only
accepted it positionally — passing `-d` errored with
`flag provided but not defined: -d`.

This adds `-d` / `--description` to both `comments` subcommands so every
body-bearing command shares one flag.

### Behaviour / precedence

Unchanged for existing usage. Body resolution is now:

1. positional argument (kept first for back-compat),
2. `-d` / `--description`,
3. piped stdin,
4. `$EDITOR` (interactive only).

### Testing

- `go build`, `go vet ./...`, `go test -short ./cmd/... ./modules/...` all pass.
- Manually verified `tea comments add --help` / `edit --help` list the flag,
  and that `-d` resolves the body (reaches the API, no parse error, no editor
  prompt, no stdin block).

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-on: https://gitea.com/gitea/tea/pulls/1043
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Brien Coffield <coffbr01@gmail.com>
Co-committed-by: Brien Coffield <coffbr01@gmail.com>

cmd/comments/body_test.go

@@ -0,0 +1,101 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package comments
+
+import (
+	"io"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestResolveBody(t *testing.T) {
+	testCases := []struct {
+		name        string
+		positional  string
+		description string
+		stdinPiped  bool
+		stdin       string
+		expected    string
+	}{
+		{
+			name:       "positional only",
+			positional: "from positional",
+			expected:   "from positional",
+		},
+		{
+			name:        "description flag only",
+			description: "from -d",
+			expected:    "from -d",
+		},
+		{
+			name:        "positional wins over description for back-compat",
+			positional:  "from positional",
+			description: "from -d",
+			expected:    "from positional",
+		},
+		{
+			name:        "description wins over piped stdin",
+			description: "from -d",
+			stdinPiped:  true,
+			stdin:       "from stdin",
+			expected:    "from -d",
+		},
+		{
+			name:       "piped stdin used when nothing else given",
+			stdinPiped: true,
+			stdin:      "from stdin",
+			expected:   "from stdin",
+		},
+		{
+			name:       "stdin ignored when not piped (interactive terminal)",
+			stdinPiped: false,
+			stdin:      "should never be read",
+			expected:   "",
+		},
+		{
+			name:       "empty when no source provided",
+			stdinPiped: false,
+			expected:   "",
+		},
+		{
+			name:       "piped but empty stdin yields empty body",
+			stdinPiped: true,
+			stdin:      "",
+			expected:   "",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			body, err := resolveBody(tc.positional, tc.description, tc.stdinPiped, strings.NewReader(tc.stdin))
+			require.NoError(t, err)
+			assert.Equal(t, tc.expected, body)
+		})
+	}
+}
+
+// TestResolveBodyDoesNotReadStdinWhenBodyGiven guards the original bug: when a
+// body is supplied positionally (or via -d), stdin must not be consumed, so the
+// command can never block on a non-TTY stdin under CI / agent harnesses.
+func TestResolveBodyDoesNotReadStdinWhenBodyGiven(t *testing.T) {
+	reader := &trackingReader{}
+
+	body, err := resolveBody("positional body", "", true, reader)
+	require.NoError(t, err)
+	assert.Equal(t, "positional body", body)
+	assert.False(t, reader.read, "stdin must not be read when a body is supplied")
+}
+
+// trackingReader records whether Read was ever called.
+type trackingReader struct {
+	read bool
+}
+
+func (r *trackingReader) Read(p []byte) (int, error) {
+	r.read = true
+	return 0, io.EOF
+}