feat: add statistics to the archive

[vycdev2]

Summary

• aggregate project statistics across every item after the Archive header, including peer and nested archived projects
• preserve normal project boundaries while allowing the Archive scope to continue to the end of the document
• add regression coverage and document the user-visible enhancement

Verification

• npm test — passed: 136 tests
• npm run compile — passed: webpack development build completed
• npm run format:check — passed: all matched files use Prettier style
• git diff --check — passed

Risk

• Low: the change reuses existing project token aggregation and only widens the configured Archive header scope.

Closes #87

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