feat(statistics): transcript timeline (segments, percentiles, parallel flags, idle)

[efirvida]

Chain Context

Field	Value
Chain	per-session statistics module (upstream Gentleman-Programming#1583)
Tracker	upstream/statistics-tracker → upstream integration PR Gentleman-Programming#1627 (draft)
Position	10 of 27
Base	upstream/statistics-09-aggregate-tests
Depends on	#37
Follow-up	upstream/statistics-10-timeline (slice 11)
Review budget	366 / 400
Starts at	upstream/statistics-09-aggregate-tests
Ends with	feat(statistics): transcript timeline (segments, percentiles, parallel flags, idle)

Chain Overview

upstream/main
 └── upstream/statistics-tracker (root, integration PR #1627)
      └── … slices 1..9 … (##37 is the immediate parent)
           └── 📍 upstream/statistics-10-timeline
                └── … slices 11..27 …

Scope

• Includes: feat(statistics): transcript timeline (segments, percentiles, parallel flags, idle)
• Excludes: every other slice. A polluted diff against upstream/statistics-09-aggregate-tests is a branching bug, not a scope surprise.

Verification

Focused and affected suites are green on this slice; tests and docs for this unit ship with it.