Move handoff routing and ownership rules out of per-agent system
prompts and into the Agent Framework handoff builder guidance.
This keeps AgentInstructionComposer focused on Aryx-owned system
prompt content while letting WithHandoffInstructions supply the
workflow-level handoff semantics.
- remove handoff-mode runtime guidance from AgentInstructionComposer
- expand HandoffWorkflowGuidance with the triage/specialist rules
- update tests to pin the new split of responsibilities
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
