[tonyfresher]

Cloud workspaces now have sharing and presence enabled by default. The top-right menu lets owners invite people by email, see members and pending invitations together, and remove members or revoke invitations. Active avatars keep the existing header styling and let you jump to another user's current page.

Design reference: workspace sharing draft in Figma.

• Replaces the experimental collab / MOI_COLLAB flag and init --collab opt-in with the cloud environment. Local installs have no sharing menu or live presence; cloud workspace setup installs COLLAB.md and collaboration declarations by default.
• Groups collaboration code into members, presence, and sharing, keeping identity separate and preserving the public applet API.
• Reuses the membership API and mutation hooks. Invitations clear the input immediately, use toasts for success/errors/duplicates, and restore the address after a failed request. Loading and retry states remain available.
• Uses one member ordering for the popup and active avatars. Member rows show names and emails; avatar tooltips show the current page. Unknown pages don't navigate, and your avatar opens sharing.

Agent invitations remain commented out until the backend supports them. Linked-workspace routing and cross-machine presence are outside this change.

Validation: 222 related unit/integration tests passed, plus typecheck, lint, and repository checks. Consolidated sharing visual coverage into two tests with three captures: member popup, active-page tooltip, and duplicate-invitation toast. Visual tests cover appearance and sharing controls; navigation is covered by component and navigation tests because the visual harness uses an in-memory router.

[molefrog]

Checked locally, works well!