Business Needs: Team isolation, namespace control, security/audit

Just putting some ideas out there.

Keybase is great for casual group chat and working with unaffiliated rogue operatives. For business use, we need:

1. isolation from outsiders (at least in the client)
- we cannot have employees, in the same screen, easily moving between personal messages and business messages
- we cannot have people getting phished in DMs from people with similar usernames to team members
- when we kick someone, they need to lose access to team channels, team DMs, files immediately.
- ideally, they have a separate set of keys from their own personal user profile/other teams

2. control of the namespace
- to enforce name policies, ensure availability of good, meaningful names
- to allow users to have different identities between teams
- to revoke and reassign names

3. ability to audit activity and enfoce certain security features, like lockdown mode

Possible solutions:
- Teams roll their own clients with some hard coded name assignments to keys, contact whitelisting
- move to a more Slack-like setup where everything is a team, vanilla Keybase is the Keybase (Open) Team, user needs to switch between teams to see other messages
- move to a Protonmail-like setup with sub accounts controlled by the master admin

See also #166 and #3233

No files, tests, or entry points are named; begin by reviewing related issues #166 and #3233 and the proposed team-isolation approaches. Before implementation, the requirements need a concrete decision and defined scope for namespace control, access revocation, auditing, and security enforcement.

Written by the indexing model from the issue text.