feat: Add list-scopes command using inventory architecture

[Copilot]

Summary

Rebuilds the list-scopes command from closed PR #1487 using the new inventory system. The command lists required OAuth scopes for enabled tools, helping users determine token permissions needed.

Why

PR #1487 was closed due to significant architectural changes (inventory refactor). This feature remains valuable for understanding scope requirements across toolsets.

What changed

• Added cmd/github-mcp-server/list_scopes.go - command implementation using inventory API
• Added script/list-scopes - convenience wrapper script
• Extracted formatToolsetName helper to cmd/github-mcp-server/helpers.go (shared with generate_docs.go)

Implementation is 74 lines shorter than original (290 vs 364) - no mock clients needed, uses inventory filtering directly.

MCP impact

• No tool or API changes - This is a CLI utility command, not an MCP tool

Prompts tested (tool changes only)

N/A - CLI command only

Security / limits

• No security or limits impact - Read-only command that queries tool metadata

Tool renaming

• I am not renaming tools as part of this PR

Lint & tests

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

Docs

• Not needed - CLI utility, not user-facing tool

Usage

# Default toolsets
$ github-mcp-server list-scopes --output=summary
Required OAuth scopes for enabled tools:
  read:org
  repo
Total: 2 unique scope(s)

# All toolsets
$ github-mcp-server list-scopes --toolsets=all --output=summary
Total: 7 unique scope(s)

# JSON output for automation
$ github-mcp-server list-scopes --output=json

Supports all stdio command flags (--toolsets, --read-only, --tools) and three output formats (text, json, summary).

Original prompt

Please rebuild http://github.com/github/github-mcp-server/pull/1487 based on main with new scope handling features, it has changed a lot, but this could be a useful feature and I'd like a fresh PR that takes this approach and makes a simple solution, since the refactor makes it much cleaner with inventory and things.

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[JoannaaKL]

@copilot create a stacked pr based on this one to:
pass a pat to script/list-scopes script and compare scopes in it vs required by tools. The command to list scopes in a PAT token:

curl -sI -H "Authorization: Bearer $GITHUB_PERSONAL_ACCESS_TOKEN" \
  https://api.github.com/user | grep -i x-oauth-scopes