Post-v1: drag a lap marker on the marshaling graph to re-time it (preview until commit)

[ryan-johnson2]

User request (2026-07-04), post-v1. The marshaling RSSI graph's lap markers should be draggable horizontally to re-time that lap's gate pass — the same interaction language as the enter/exit threshold handles.

Ground rules (established by the tune-detection work, #348/#354):

• Nothing reaches the log until an explicit Commit — dragging adjusts a local preview only (the lap's new time, and the knock-on durations of the adjacent laps, since a pass bounds two laps). Preview styling consistent with the unified diff list (green/red).
• Commit maps to the existing auditable primitive — AdjustLap { target: <pass end_ref>, at } — so it lands in the audit trail and is reversible like any ruling.
• Respects the Final lock (Marshaling: an official (Final) result is locked — Revert to marshal (protests exempt) #356): official results can't be dragged; the banner/Revert ceremony applies.
• The drag handle must be top-of-paint-order and not conflict with marker CLICK (select lap) — likely a small grab affordance on the marker head vs. the line body, or drag-threshold discrimination (click = select, drag past N px = re-time).

Related: #355 (timer tune page shares the drag interaction), #357-adjacent marshaling declutter.