✨ feat: add --body-file support to PR review write actions

[ShigureNyako]

Motivation

gh-llm pr review-submit already supports --body-file, but the other PR review write commands still required inline --body text. That makes thread replies and inline review messages awkward for multi-line Markdown, quoted replies, and shell-safe automation.

This PR closes that gap for issue #20 while keeping the scope limited to the three commands covered there, leaving the broader input-consistency follow-up in #28 unchanged.

Changes

• add mutually exclusive --body / --body-file inputs for:
  • gh-llm pr thread-reply
  • gh-llm pr review-comment
  • gh-llm pr review-suggest
• reuse the existing file/stdin loading behavior so --body-file - reads from standard input
• keep review-suggest default behavior intact by falling back to Suggested change when no body input is provided
• document the new file/stdin workflow in README.md
• add CLI tests covering file input, stdin input, suggestion-body composition, and mutual-exclusion validation

Validation

• uv run ruff format --check src/gh_llm/commands/pr.py tests/test_cli.py
• uv run ruff check .
• uv run pyright src/gh_llm tests
• uv run pytest -q
• prettier --check README.md

Related Issues

• Closes feat: 为 thread-reply / review-comment / review-suggest 增加 --body-file 支持 #20
• Follow-up scope remains in 在 #20 之外，继续补齐 comment-edit / suggestion-file / stdin 的写入输入一致性 #28

[ShigureNyako]

Self-reviewed the diff and PR description.

@SigureMo Please review this PR when you have time. Thanks!

[Copilot]

Pull request overview

Adds --body-file (including stdin via -) support to PR review write commands so multi-line Markdown bodies can be provided safely without shell-escaping, aligning these commands with existing pr review-submit --body-file behavior.

Changes:

• Add mutually exclusive --body / --body-file flags for pr thread-reply, pr review-comment, and pr review-suggest.
• Reuse shared body resolution logic so --body-file - reads from standard input.
• Extend CLI tests and README examples to cover file/stdin usage and suggestion body composition.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/gh_llm/commands/pr.py	Adds --body-file flags and shared _resolve_body_argument() to load body from file/stdin across PR write commands.
tests/test_cli.py	Adds tests for --body-file (file + stdin), suggestion body composition, and mutual exclusion handling.
README.md	Documents --body-file workflows for thread replies, review comments, suggestions, and stdin piping.

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[Copilot]

This assertion depends on argparse’s exact error string, which can change between Python/argparse versions (or even reorder option names). To avoid brittle failures, assert more loosely (e.g., check for not allowed with argument and the presence of both --body and --body-file), rather than the full formatted message.

Suggested change

	assert "argument -F/--body-file: not allowed with argument --body" in err
	assert "not allowed with argument" in err
	assert "--body" in err
	assert "--body-file" in err

[ShigureNyako]

结论：COMMENT（从代码质量判断，这个 PR 我会给出 APPROVE；但当前登录账号与 PR 作者相同，GitHub 不允许对自己的 PR 直接提交 APPROVE，因此这里用 COMMENT 形式提交正式 review。）

我独立检查了这次改动，重点看了功能设计、CLI 交互、一致性、边界行为、测试覆盖和文档。

结论依据：

• 功能设计：实现范围与 #20 对齐，只补齐 thread-reply / review-comment / review-suggest 的 --body-file，没有把 #28 的更大范围输入一致性改动混入当前 PR，scope 控制合理。
• CLI 交互与一致性：三个命令都统一为 --body / --body-file 互斥；--body-file - 复用了现有 stdin 读取语义，与 review-submit 保持一致。
• 边界行为：review-suggest 在未提供正文时仍回退到 Suggested change，兼容现有默认行为，没有看到回归风险。
• 测试覆盖：新增了 file 输入、stdin 输入、suggestion 组合，以及互斥参数校验相关测试。
• 文档：README 已补充典型示例，并明确说明可通过 --body-file - 从标准输入读取多行内容。

我还在本地基于该 PR 代码验证了：

• uv run pytest -q
• uv run ruff check .
• uv run pyright src/gh_llm tests
• prettier --check README.md

目前没有看到阻塞合并的问题。#28 中剩余的输入一致性补齐仍可作为后续独立工作继续推进。

[SigureMo]

LGTMeow