Support attaching Foundry Skills to toolbox versions in azd ai toolbox

[hund030]

What

azd ai toolbox should support attaching Foundry Skills as references on toolbox versions, per the new optional skills field on ToolboxVersionObject and CreateToolboxVersionRequest in the Foundry data-plane spec.

Why

Toolboxes are the unit agents reference at run time; skills are pre-authored capability snippets users want to reuse across toolboxes. Today users have to hand-edit the JSON payload to attach a skill, then drive createToolboxVersion directly. The CLI should make this a first-class operation.

Scope

• toolbox create --from-file: accept an optional skills[] block alongside connections[].
• New azd ai toolbox skill subgroup with add, remove, and list verbs, mirroring the existing connection subgroup. Each mutation publishes a new immutable toolbox version (no dedicated REST endpoint for per-skill mutation).
• connection add / connection remove: carry skills forward verbatim into the new version.
• toolbox show / toolbox version list: surface the new field.

Out of scope

• policies / rai_config field on ToolboxVersionObject — separate follow-up.
• Other ToolboxSkill discriminator variants beyond skill_reference — none defined in the spec today.

References

• Foundry toolbox spec: https://github.com/Azure/azure-rest-api-specs/blob/feature/foundry-release/specification/ai-foundry/data-plane/Foundry/src/toolboxes/models.tsp