Add bulk/batch issue label operations

审查现有的 issue_write MCP 工具以及用于向 issue 添加 labels 的 GitHub REST 端点。比较提议的 batch_update_issues 工具与扩展 issue_write 的方案，然后定义单次调用应如何通过添加和移除操作处理多个 issue 编号，并验证已记录的工作流。

[!Note]
Responses generated with Claude

Describe the feature or problem you'd like to solve

There is no way to add labels to multiple issues in a single MCP tool call. The current issue_write tool supports labeling one issue at a time, but common workflows require labeling dozens of issues matching a search query (e.g., "label all issues from milestone X as priority/high").

This forces MCP clients to either:

1. Make N sequential issue_write calls (slow, noisy)
2. Fall back to gh CLI with scripting (breaks MCP-first pattern)

Proposed solution

Add a batch labeling capability — either as:

Option A: A new batch_update_issues tool that accepts a list of issue numbers and label operations:

{
  "owner": "org",
  "repo": "repo",
  "issue_numbers": [1, 2, 3, 4, 5],
  "add_labels": ["priority/high"],
  "remove_labels": ["needs-triage"]
}

Option B: Extend issue_write with a batch method that accepts multiple issue numbers.

Example prompts or workflows

1. "Add the stale label to all issues that haven't been updated in 90 days"
2. "Label issues #10, #15, #20, #25 as sprint-42"
3. "Move all needs-triage issues to triaged after review"
4. "Add breaking-change label to all issues in the v3.0 milestone"

Additional context

The GitHub REST API supports adding labels to individual issues via POST /repos/{owner}/{repo}/issues/{issue_number}/labels. A batch tool would simply iterate internally, but having it as a single MCP call reduces round-trips and permission prompts for MCP clients like Claude Code.