Add hidden projects with subdued display

[andersonkrs]

Summary

Add support for hiding certain projects from default tree view and list pickers, while still allowing them to appear in a secondary view or via a shortcut with a subdued (faded gray) style.

Motivation

Users often have projects they are not actively working on but still want quick access. Hiding them reduces clutter while keeping them reachable when needed.

Proposed behavior

• Add a config flag to mark a project as hidden (name TBD).
• Hidden projects are excluded from default tree view and picker lists.
• Provide a toggle or shortcut to show hidden projects on demand.
• When shown, render hidden projects with a subdued color (e.g., faded gray) to distinguish them.

Acceptance criteria

• Config parsing supports a hidden flag per project.
• Default tree view/pickers exclude hidden projects.
• Users can reveal hidden projects via a toggle/shortcut.
• Hidden projects are styled with a clear visual distinction.

Notes

• Ensure the hidden state is per-project and does not affect normal session behavior.