docs(readme): restore comprehensive architecture details and position stellar integration lower in doc

[0dillon]

Summary of Changes

• Restored Complete Technical Architecture: Brought back all exhaustive documentation sections from the original README, including core engine mechanics, workspace/sub-crate breakdown, architecture diagrams, sequence charts, deep dive technical rationale, and setup/simulation guides.
• Repositioned Stellar & Soroban Architecture: Moved the Stellar and Soroban architecture integration section lower in the document beneath the core problem statements, system architectures, and deep dives, rather than leading with it at the top of the README.
• Maintained Clean Engineering Style: Preserved professional, authentic badge layout and formatting standards.

[enny791]

LGTM! Complete architectural documentation restored, with Stellar and Soroban integration correctly repositioned lower in the document hierarchy.