Add scenario provisioning steps

[bill-ph]

Summary

• add the scenario provisioning client for provision/status/deprovision control-plane APIs
• add provision, wait-ready, and deprovision step executor support with in-memory state
• add redaction and classified errors so cleanup failures and timeouts are clear in artifacts

Tests

• go test -count=1 ./tests/scenario/...
• just lint

Review

• Ran one review pass and fixed the findings around cleanup idempotency, context cancellation, strict wait-option parsing, and bearer-token redaction.

[github-actions]

Test Impact Plan

Deterministic summary of how this PR changes tests, CI runners, and coverage-risk signals.

Summary

Area	Added	Changed	Deleted
Test files	6	2	0
E2E/journey files	0	0	0
Workflow files	0	0	0

Signals

• Test cases: +14 / -0
• Assertions: +100 / -0
• Skips or known failures added: 0
• Workflow continue-on-error added: 0
• Workflow path filters added: 0
• Test commands removed from justfile: 0
• E2E/journey retry lines added: 0

Coverage risk: neutral or increased

No coverage-reduction warnings detected.