Make crypto reconstruction methodology prominent

[tradingexpert]

Summary

• define one venue-, asset-class-, and vendor-independent replay boundary with two explicit fidelity paths: observed MBO and reconstructed virtual MBO
• document Databento and Binance as the current reference integrations, not permanent project boundaries
• make the merged L2-to-virtual-MBO capability prominent near the top of the README
• publish the full-capture evidence: 99.9708% of valid trades aligned, all processed depth endpoints reconciled, and all joinable book-ticker states matched
• explain why evidence-constrained virtual MBO enables crypto replay without presenting inferred queues as exchange-native MBO
• define a measurable Crypto Realism Challenge based on paired L2/L3 or live passive-fill outcomes
• align architecture, assumptions, connector, data, contributor, and release documentation with that positioning

Why a separate PR

PR #61 merged the reconstruction implementation at eb5ae67. This documentation commit was prepared after that merge, so this clean follow-up branch is based on current main and contains only the post-merge positioning work.

Validation

• documentation-only diff against current main
• git diff --check passes
• local suite: 252 passed, 13 skipped, 96.87% total branch coverage (native-extension cases are exercised in CI)

Community benchmark: #62