feat(ux): add progress spinner for long-running commands

[fredaluliu]

Background

Long-running commands like instance create, tool create currently show no progress feedback. Users see a blank screen for 5-10 seconds without knowing if the CLI is working or hung.

Proposal

Add a progress spinner for commands that take >2s, with -o json silencing:

• Define ProgressFunc(step string, status Status) callback
• Text mode: show spinner (e.g. via pterm library) with step description
• -o json mode: spinner is no-op, stdout stays pure JSON
• On completion: replace spinner with checkmark/cross

Affected Commands

• agr instance create (waiting for instance to start)
• agr tool create (waiting for tool to become ACTIVE)
• agr instance debug (creating debug tool + waiting)
• agr pre-cache-image-task create (submitting task)

Expected Behavior

$ agr instance create --tool-id sdt-xxx
⣾ Creating instance...
✓ Instance created: sandbox-abc123

$ agr instance create --tool-id sdt-xxx -o json
{"SchemaVersion":"agr.v1", ...}

Implementation Notes

• Go library: pterm or briandowns/spinner
• Spinner writes to stderr (never pollute stdout)
• Respect --no-color and NO_COLOR env
• Respect --non-interactive (no spinner)

Category

UX / Safety