feat(shell): billable hours report (config, rounding, pure report builder, collection)

[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	23 of 27
Base	upstream/statistics-22-panel-readability
Depends on	#50
Follow-up	upstream/statistics-23-billable-report (slice 24)
Review budget	313 / 400
Starts at	upstream/statistics-22-panel-readability
Ends with	feat(shell): billable hours report (config, rounding, pure report builder, collection)

Chain Overview

upstream/main
 └── upstream/statistics-tracker (root, integration PR #1627)
      └── … slices 1..22 … (##50 is the immediate parent)
           └── 📍 upstream/statistics-23-billable-report
                └── … slices 24..27 …

Scope

• Includes: feat(shell): billable hours report (config, rounding, pure report builder, collection)
• Excludes: every other slice. A polluted diff against upstream/statistics-22-panel-readability 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.