Add sort and order parameters to search_repositories tool

[kerobbi]

This PR adds explicit sort and order params to the search_repositories tool to align with other search_* tools, especially as the relevant REST API endpoint does accept them. Additionally, it adds server instructions for search_* tools related to sorting functionality.

Changes

• Added sort param with enum values: stars, forks, help-wanted-issues, updated
• Added order param with enum values: asc, desc
• Added server instructions for sort and order usage in search_* tools

Closes: #1178

[Copilot]

Pull Request Overview

This PR adds explicit sorting parameters to the search_repositories tool to improve model clarity when sorting search results. It aligns the tool's interface with other search tools by exposing the GitHub API's native sorting capabilities.

• Added sort parameter with enum values for different sorting criteria (stars, forks, help-wanted-issues, updated)
• Added order parameter with enum values for sort direction (asc, desc)
• Updated tests and documentation to reflect the new parameters

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
pkg/github/search.go	Implements the new sort and order parameters in the tool definition and request handling
pkg/github/search_test.go	Adds test coverage for the new parameters in both schema validation and API call verification
pkg/github/toolsnaps/search_repositories.snap	Updates the tool schema snapshot to include the new parameter definitions
README.md	Documents the new sort and order parameters in the tool reference

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