Implement scenario draft creation, timeline workspace, and step editing workflows

[kalen-releasedgroup]

Summary

Give authors a usable editor to turn captured steps into an intentional scenario.

Scope

• Create draft scenarios from completed recordings.
• Implement the timeline workspace with step ordering, badges, confidence signals, and detail inspection.
• Support delete, suppress, reorder, note/rationale, variable-driven marking, and locator-candidate switching.

Requirement Links

• FR-AUTH-001, FR-AUTH-002
• Section 9.3
• Acceptance Criterion 2

Dependencies

• Normalized steps and locator candidates
• Blazor shell

Exit Criteria

• Authors can review and edit steps entirely through the UI.
• Timeline operations update draft scenario state, not committed history.
• Step details expose the evidence needed to make editing decisions.