adding labels tools

[tonytrg]

This PR adds label management tools using a consolidated approach with GraphQL-only operations.

Resolves#312

Summary

Following the tool consolidation pattern from #1172, this PR introduces three multi-functional label management tools:

• get_label - Retrieves a specific label by name from a repository
• list_label - Lists labels from a repository OR an issue (uses issue_number parameter to switch context)
• write_label - Unified write operations with method parameter:
  • create - Create a new label (requires name, color)
  • update - Update existing label (requires name, at least one of new_name/color/description)
  • delete - Delete a label (requires name)

Design Philosophy

We're moving toward consolidated, multi-functional tools that use method parameters to handle related operations, rather than creating separate tools for each action. This approach:

• Reduces tool proliferation and context window usage
• Groups related functionality logically
• Makes the API more intuitive (similar to Consolidating pull requests get tools #1172's PR consolidation)

Technical Details

All operations use GraphQL exclusively (gqlClient) for consistency and efficiency:

• Queries use repository.labels and repository.issue.labels
• Mutations use createLabel, updateLabel, and deleteLabel
• Helper functions getRepositoryID() and getLabelID() support the mutations

[Copilot]

Pull Request Overview

This PR adds comprehensive GitHub Labels tools functionality to the GitHub MCP Server, enabling users to create, read, update, and delete repository labels through dedicated tools.

• Introduces a new "labels" toolset with three core functions: get_label, list_label, and write_label
• Adds extensive test coverage for all label operations including edge cases and error scenarios
• Updates documentation to include the new labels toolset in both README and remote server documentation

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
pkg/github/tools.go	Adds ToolsetLabels metadata and integrates label tools into the default toolset group
pkg/github/labels.go	Implements the three main label tools with GraphQL operations for CRUD functionality
pkg/github/labels_test.go	Comprehensive test suite covering all label operations and error cases
pkg/github/toolsnaps/*.snap	Tool schema snapshots for the three label tools
docs/remote-server.md	Documents the new labels toolset in the remote server table
README.md	Updates tool documentation with labels section and individual tool descriptions

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