feat: add chat.createGroupChat tool for multi-person group conversations

[allenhutchison]

Summary

The current Chat tools support 1:1 DMs (chat.sendDm, chat.findDmByEmail) and named spaces (chat.setUpSpace), but there's no way to create unnamed multi-person group conversations — the GROUP_CHAT spaceType in the Google Chat API.

Context

Google Chat supports three space types:

• DIRECT_MESSAGE — 1:1 conversations (supported via chat.sendDm)
• SPACE — named group spaces (supported via chat.setUpSpace)
• GROUP_CHAT — unnamed multi-person conversations (❌ not supported)

Group chats are the unnamed conversations you see in Google Chat when you start a conversation with multiple people without creating a formal space (e.g. https://mail.google.com/chat/u/0/#chat/space/AAQAjCNSsU0).

Proposed Solution

Add a chat.createGroupChat tool (or extend chat.setUpSpace) that calls spaces.setup with:

• spaceType: 'GROUP_CHAT'
• No displayName (group chats are unnamed)
• A list of member emails or user IDs

API Details

The spaces.setup API already supports this. From the docs:

• Set Space.spaceType to GROUP_CHAT
• Do not set Space.displayName
• Specify memberships as users/{email} or users/{userId}
• Up to 49 additional users can be added
• Google Groups are not supported in group chats (only in named spaces)
• The authenticated user is automatically included

Implementation Notes

• The existing _setupDmSpace in ChatService.ts is a good reference — it already uses spaces.setup for DIRECT_MESSAGE
• Could either add a new createGroupChat method or make setUpSpace accept an optional spaceType parameter
• Update the Chat skill to document the new capability

Related

• Discovered during PR feat: add Chat skill for Google Chat messaging guidance #249 (Chat skill)