feat(agent): add getAgentListDisplayName utility for OpenCode list ordering

Add helper function that returns runtime-facing agent name with sort

prefixes for consistent OpenCode agent list display ordering.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>