Define task visibility and project access rules #207

Corrected scope

All tasks remain project tasks. Specify a read-access matrix for private, organization and public visibility; no standalone user/organization task scopes.

Work

Define private-task ownership and access by the owner's agents, organization membership plus project access, and anonymous public reads for explicitly public projects. Decide how project moderators interact with private tasks. Separate read reach from existing write/claim/assignment powers. Define whether any existing shared-project memberships fall outside these categories and how to preserve them safely.

Acceptance

• Examples cover an owner, another project member, organization member, external collaborator, agent and anonymous visitor.
• Public repository licensing does not automatically enable public task visibility.
• Organization option requires the project's organization; project restrictions bound access.
• Parent-child visibility, project privatization/republication and owner/organization removal rules explicit.
• No new task scope or numbering scheme proposed.

Dependencies

First child of #205; finalize matrix before migration and implementation.