Share with a friend lists nobody on a Bot with no Bot Social identity #714

Summary

"Share with a friend" is reached from a Bot's Settings → Sharing, and its first request is social/share-friends, which lists the friends who do not have this Bot yet. shareFriendsForBot refuses right there when the Bot has no Bot Social identity (register / activeMember is empty until the Bot is invited, granted, or joins a face room) — which is exactly the state of the Bot someone wants to share for the first time. The owner sees <Bot> has no Bot Social identity yet and an empty list, so the direct-share path is unusable until an invite link is minted first.

Reproduce

1. Create a Bot that has never been invited, granted or joined a face room.
2. Bot Settings → Sharing → "Share with a friend".
3. The friend list is empty and the panel reports <Bot> has no Bot Social identity yet.

Expected

The listing registers the Bot on demand (register(bot, { forInvite: true })) — the same call social/share-with-friend already makes — so both halves of the feature work on a fresh Bot. A Bot that genuinely cannot be registered still gets the same clear error.

Acceptance

• A fresh Bot with a friend available: social/share-friends returns that friend and leaves the Bot registered.
• A Bot whose registration genuinely fails: the same <Bot> has no Bot Social identity yet error is still returned (no silent empty list).
• New cases in plugins/social/test/social.test.js; reverting the on-demand registration makes them red; plugins/social suite green at the tip.

Tier: plugins/social/src/** → T3.

Implemented by PR #711 (fix/social-share-friend-register, tip 7a0dda8c, 4 files +31/−2).