Expose task visibility in MCP contracts, discovery and recall #210

Work

Keep projectId + canonical number contracts. Add documented visibility inputs/outputs and optional list filters without granting access through a filter. Explain private defaults, subtask inheritance, organization constraints and public-project eligibility in tools/list, system_memory and examples. Update partial/replacement update semantics coherently.

Acceptance

• Agents can create a private project task and explicitly choose another allowed visibility.
• Existing project-only requests remain valid with documented safe defaults.
• Recall, task_ready, item_resolve and search/list results reveal only readable tasks.
• Changing visibility cannot be confused with moving a task to another scope/project.
• Unknown and inaccessible task responses do not expose content or metadata.

Dependencies

#209 access services; preserve existing numbering and assignment-reference contracts.