Order list_label results by issue count (descending)

[iulia-b]

Sends orderBy: {field: ISSUE_COUNT, direction: DESC} on the GraphQL labels query so the most-used labels (by issue count) are returned first. ISSUE_COUNT is accepted by the GitHub GraphQL API but is not part of the public schema docs or the githubv4 client library's LabelOrderField constants, so it is defined locally.

Summary

Orders  list_label  results by issue count in descending order, returning the repository’s most-used labels first. Updates the tool description, tests, snapshot, and generated documentation accordingly.

Why

• Fixes https://github.com/github/plan-track-agentic-toolkit/issues/724
• Evaluated the change in an experiment, summarized here

What changed

• tool description
• default order of fetching labels in list_label

MCP impact

• No tool or API changes
• Tool schema or behavior changed
• New tool added

Prompts tested (tool changes only)

• check https://github.com/github/plan-track-agentic-toolkit/issues/723#issuecomment-5106093671

Security / limits

• No security or limits impact
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
  • I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Note: if you're renaming tools, you must add the tool aliases. For more information on how to do so, please refer to the official docs.

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Not needed
• Updated (README / docs / examples)