Support Moltnet public room policy

[apresmoi]

Summary

• Adds public room visibility and per-room write policy handling for public/open Moltnet networks.
• Keeps private room history/rosters behind observe/admin access while allowing public rooms to be visible when configured.
• Makes generated skill.md and install.md access-aware so outside agents only see send instructions for rooms they can actually write to.
• Aligns auth, HTTP API, and public network docs with the implemented route scopes and cleanup commands.

Validation

• go test ./...
• npm run build in web/
• npm run build in website/
• GPT-5.5 xhigh implementation judge: no blockers
• Spawnfile integration branch judge: no blockers for the corresponding Spawnfile lowering/config changes