feat(statistics): markdown, CSV and JSON exporters, with the v1 contract docs

[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	16 of 27
Base	upstream/statistics-15-rpc-tests
Depends on	#43
Follow-up	upstream/statistics-16-exporters-and-contract (slice 17)
Review budget	267 / 400
Starts at	upstream/statistics-15-rpc-tests
Ends with	feat(statistics): markdown, CSV and JSON exporters, with the v1 contract docs

Chain Overview

upstream/main
 └── upstream/statistics-tracker (root, integration PR #1627)
      └── … slices 1..15 … (##43 is the immediate parent)
           └── 📍 upstream/statistics-16-exporters-and-contract
                └── … slices 17..27 …

Scope

• Includes: feat(statistics): markdown, CSV and JSON exporters, with the v1 contract docs
• Excludes: every other slice. A polluted diff against upstream/statistics-15-rpc-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.