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.go

@@ -0,0 +1,73 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package flags
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	"golang.org/x/term"
+)
+
+// stdinPiped reports whether stdin is not a terminal, e.g. when a description
+// is piped from a file, command substitution, or a CI harness.
+func stdinPiped() bool {
+	return !term.IsTerminal(int(os.Stdin.Fd()))
+}
+
+// resolveCreateBody returns the issue/PR description for create commands.
+//
+// Precedence:
+//  1. --description-file (read from the file, or stdin when the path is "-")
+//  2. --description
+//  3. piped stdin
+func resolveCreateBody(description, descriptionFile string, descriptionFileSet, stdinPiped bool, stdin io.Reader) (string, error) {
+	if descriptionFileSet {
+		return readDescriptionSource(descriptionFile, stdin)
+	}
+	if description != "" {
+		return description, nil
+	}
+	if stdinPiped {
+		return readDescriptionStdin(stdin)
+	}
+	return "", nil
+}
+
+// resolveEditBody returns the new issue/PR body when a description flag was
+// provided, or nil when the caller should leave the body unchanged.
+func resolveEditBody(description string, descriptionSet bool, descriptionFile string, descriptionFileSet bool, stdin io.Reader) (*string, error) {
+	if descriptionFileSet {
+		body, err := readDescriptionSource(descriptionFile, stdin)
+		if err != nil {
+			return nil, err
+		}
+		return &body, nil
+	}
+	if descriptionSet {
+		body := description
+		return &body, nil
+	}
+	return nil, nil
+}
+
+func readDescriptionSource(source string, stdin io.Reader) (string, error) {
+	if source == "-" {
+		return readDescriptionStdin(stdin)
+	}
+	data, err := os.ReadFile(source)
+	if err != nil {
+		return "", fmt.Errorf("could not read description file %q: %w", source, err)
+	}
+	return string(data), nil
+}
+
+func readDescriptionStdin(stdin io.Reader) (string, error) {
+	data, err := io.ReadAll(stdin)
+	if err != nil {
+		return "", fmt.Errorf("could not read description from stdin: %w", err)
+	}
+	return string(data), nil
+}