Teach agents ready-work discovery and verify multi-agent handoff #96

Work

Expose task_ready (or clearly equivalent discovery), blocker mutations and informative task_get results. Update compact descriptions, server instructions, system_memory and examples: recall -> ready -> get -> claim -> work -> complete with current versions. Include task/ticket synonyms and no-ready explanations.

Acceptance

• Fresh agent selects eligible work and reads prerequisites before claiming.
• Two agents race safely; loser refreshes rather than overwriting ownership.
• Parent/subtask, cancellation, reopen and permission cases covered by integration tests.
• Recall summarizes ready tasks and owned work within budget, without silently changing task state.

Dependencies

Ready queries, atomic claim and #82 agent-reference contract.