Feature Request: Add get_user tool to fetch a user profile by username

Start in pkg/github/context_tools.go by comparing get_me with the existing client.Users.Get call. Add the required username input while preserving the MinimalUser + UserDetails response and users tool metadata described in the issue. Done means the tool calls GET /users/{username} through the authenticated client and exposes the requested profile across GitHub environments.

Problem

There is no tool to look up a specific GitHub user's profile by username. get_me only returns the authenticated user. search_users uses the Search API which returns a minimal user object (login, id, avatar) without profile details like name, email, bio, company, etc.

Use case

I'm building a skill that adds Co-authored-by trailers to git commits. To properly attribute a collaborator, I need their display name and numeric ID from their GitHub profile to construct the trailer:

Co-authored-by: Jane Smith <12345+janesmith@users.noreply.github.com>

Currently this requires falling back to gh api users/{username}, but I want the skill to work in Claude Desktop too where the gh CLI may not be available — only MCP tools. A get_user tool would close this gap.

Workarounds and their limits

• gh api users/{username} — works but requires the gh CLI, which isn't available in Claude Desktop
• WebFetch to api.github.com/users/{username} — works for public GitHub.com users without auth, but doesn't cover enterprise managed users (EMU) or GHES, which require authentication

A proper get_user tool using the server's authenticated client would work across all environments including enterprise.

Proposed solution

A get_user tool that accepts a required username parameter and calls GET /users/{username}. Returns MinimalUser with Details — the same response shape as get_me.

The Go client already supports this: client.Users.Get(ctx, username) is the same call get_me uses, just with a non-empty username string.

Implementation notes

Nearly identical to get_me in pkg/github/context_tools.go:

• Add a username input parameter (required string)
• Pass it to client.Users.Get(ctx, username) instead of ""
• Return the same MinimalUser + UserDetails response
• Toolset: users
• Scope: read:user
• ReadOnly: true

Edited to add - this issue was co-authored by Claude and reviewed by me.