[FEATURE]: add hiddenFromCycle config option to hide agents from tab rotation

[Cretezy]

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Add a new agent config field hiddenFromCycle (hidden_from_cycle in markdown frontmatter) that hides agents from tab/shift+tab rotation while keeping them visible and selectable via /agents. Currently hidden controls both, which means hiding an agent from the agent list also removes it from tab rotation.

The new field should:

• Be separate from hidden behavior
• Keep the agent visible in /agents list
• Only exclude the agent from tab/shift+tab cycling

[github-actions]

This issue does not fully meet our contributing guidelines.

What needs to be fixed:

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[github-actions]

Thanks for updating the issue! It now follows the contributing guidelines. The needs:compliance label has been removed.