feat: support standalone toolset metadata for default expansion

[Copilot]

Summary

Enables toolset metadata with Default: true to control default toolsets even when no tools use that toolset in the OSS build (e.g., remote-only toolsets like copilot).

Why

The remote server needs copilot toolset tools enabled by default, but the previous approach of setting Default: true on metadata didn't work because processToolsets() only examined actual tools, not standalone metadata.

Closes github/github-mcp-server-remote#619

What changed

• Added SetToolsetMetadata() to inventory Builder for registering standalone toolset metadata
• Updated processToolsets() to include standalone metadata when building default toolsets list
• Registered remote-only toolsets (copilot, copilot_spaces, github_support_docs_search) via NewInventory()
• Updated test expectations to include copilot in defaults

Before:

// GetDefaultToolsetIDs() only found defaults from actual tools
// copilot toolset with Default: true but no tools → not in defaults

After:

// Standalone metadata is processed alongside tool metadata
inv := NewInventory(t).
    SetToolsetMetadata(RemoteOnlyToolsets()). // copilot now in defaults
    Build()

MCP impact

• No tool or API changes - OSS users see no change since no OSS tools use copilot toolset. Remote server benefits from declarative Default: true on metadata.

Security / limits

• No security or limits impact - Only affects which toolsets expand to when "default" keyword is used.

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 - No user-facing documentation changes required. Code comments updated.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[Copilot]

Pull request overview

This pull request enables toolset metadata with Default: true to control default toolsets even when no tools are registered for that toolset in the OSS build. This is specifically needed for remote-only toolsets like copilot that should be default but have no tools in the local server.

Changes:

• Added SetToolsetMetadata() method to the inventory Builder for registering standalone toolset metadata
• Updated processToolsets() to process standalone metadata alongside tool/resource/prompt metadata when building default toolsets
• Integrated remote-only toolsets (copilot, copilot_spaces, github_support_docs_search) into the main inventory via NewInventory()
• Updated test expectations to include copilot in default toolsets

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
pkg/inventory/builder.go	Added toolsetMetadata field and SetToolsetMetadata() method; updated processToolsets() to include standalone metadata in default toolset calculation
pkg/github/inventory.go	Registered remote-only toolsets via SetToolsetMetadata() in NewInventory()
pkg/github/tools_test.go	Updated test expectations to include copilot in default toolsets list
internal/ghmcp/server.go	Fixed whitespace formatting (trailing spaces removed)

[Copilot]

The new functionality to process standalone toolset metadata lacks dedicated unit test coverage in pkg/inventory/registry_test.go. While integration testing via pkg/github/tools_test.go verifies that copilot appears in defaults, there should be direct tests for SetToolsetMetadata() that verify: (1) standalone metadata with Default: true adds to default toolsets, (2) standalone metadata without tools still appears in available toolsets, (3) standalone metadata descriptions are properly stored, and (4) interaction with tool-based metadata (e.g., no conflicts when both exist).