Support secure graphical sudo prompts for agent commands

[ElbertePlinio]

Agent plan

Goal: let privileged PickLab provisioning and agent-run commands request user approval through the desktop without exposing the sudo password.

Checklist:

• Define Linux askpass capability detection (SUDO_ASKPASS, KDialog/Zenity, graphical session)
• Make ProvisioningStep.privileged affect execution instead of remaining metadata-only
• Invoke privileged commands with sudo -A and an explicit askpass environment
• Treat cancellation, missing GUI, and headless sessions as clear actionable errors
• Never capture, log, persist, or pipe the password through PickLab
• Add executor tests for available, unavailable, and cancelled askpass paths
• Document the Linux behavior and manual fallback
• PR/review

Validation:

• Focused executor and CLI tests
• End-to-end Linux smoke test with a harmless sudo -A -v
• Confirm command logs contain no credential material

Current status: Planned
Next action: design the privilege-execution contract around packages/cli/src/provision/executor.ts and ProvisioningStep.privileged.

[ElbertePlinio]

Pickforge integration is tracked separately in pickforge/pickforge#215. Keep the privilege-execution contract compatible across both repositories.