Improve Block Assembly service documentation accuracy and completeness

[torrejonv]

Correct technical inaccuracy where reorg threshold was documented as 5 blocks instead of the actual CoinbaseMaturity value (typically 100 blocks). Add missing documentation for implemented features including mining candidate caching, startup blocking behavior, and unmined transaction cleanup. Include No Mempool architectural design explanation and fix markdown formatting issues to pass linting requirements.

[github-actions]

🤖 Claude Code Review

Status: Complete

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Review Summary:

This PR significantly improves the Block Assembly service documentation with accurate technical corrections and comprehensive feature documentation.

Technical Accuracy Verified:

✅ Reorg threshold correction - Changed from "5 blocks" to the actual CoinbaseMaturity value (typically 100 blocks). Verified against implementation in BlockAssembler.go:1320.

✅ Startup blocking behavior - Accurately documents the unminedTransactionsLoading flag that blocks SubmitMiningSolution, ResetBlockAssembly, and GenerateBlocks during startup. Verified in Server.go.

✅ Mining candidate caching - Comprehensive documentation of the caching mechanism, timeout behavior, and cache invalidation triggers. Verified in BlockAssembler.go.

✅ Unmined transaction cleanup - Documents the periodic cleanup process that was previously undocumented. Verified implementation exists.

✅ No Mempool Design - Adds valuable architectural context explaining Teranode's design differences from traditional Bitcoin nodes.

Formatting Improvements:

✅ Consistent markdown section numbering
✅ Fixed image path formatting
✅ Improved list formatting for better readability

Conclusion:

All technical claims in this documentation update are accurate and match the actual implementation. The PR resolves a significant technical inaccuracy (reorg threshold) and fills important documentation gaps for production features. No issues found.