pull_request_read get_files always returns full patches

从 get_files 方法的 pull_request_read 入口点开始，检查当前无条件填充 MinimalPRFile.Patch 的 convertToMinimalPRFiles。比较现有的字段选择机制 listPullRequestsItemFieldEnum 和 listCommitsItemFieldEnum，然后确认调用方可以请求不含补丁的文件元数据，并且默认行为仍然清晰。

Describe the bug

pull_request_read with method: get_files always includes the full patch for every file, and offers no way to ask for filenames only. A 21-file pull request returned roughly 370 KB when only the paths were needed.

In the source, convertToMinimalPRFiles populates MinimalPRFile.Patch unconditionally, and get_files has no field-selection parameter. Several other tools do have one, for example listPullRequestsItemFieldEnum and listCommitsItemFieldEnum, so the mechanism already exists elsewhere in the codebase.

Affected version

Unknown. Observed through a hosted GitHub MCP integration on 2026-09-06, where the server version is not exposed to me. The code references above are from the repository's default branch on that date and may not match the build that was serving the request.

Steps to reproduce the behavior

1. Call pull_request_read with method: get_files for a pull request touching a reasonable number of files.
2. Observe that every entry carries its full patch, with no option to omit it.

Expected vs actual behavior

Expected: a way to request file metadata without patches, for example a fields parameter matching the pattern used by the list tools.

Actual: patches are always included, so a caller that only needs the list of changed paths pays the full diff in context.

Possibly related to #2122, which is closed but describes the same class of oversized pull_request_read payloads.

Logs

None captured beyond the returned payload size.