Expand README with project overview

[rosasurfer]

Changes and PR have been generated by ChatGPT Codex.

Motivation

• Provide a comprehensive architecture and onboarding document that explains the repository's MT4-first design and MQL dialect distinctions (MQL4.0, MQL4.5, MQL5).
• Make intentional design choices explicit (triplicated rsfHistory1/2/3 libraries, rsfMT4Expander.dll boundary, legacy init()/start()/deinit() lifecycle) to reduce accidental regressions when modifying core code.
• Improve the top-level README.md so contributors can quickly find compile instructions, subsystem descriptions, and configuration/contribution guidance.

Description

• Add CODEBASE_ANALYSIS.md with an executive summary, detailed analysis of mql40 subsystems, history libraries, logging/error-handling, three-layer configuration model, and contributor guidance.
• Update README.md to include a clear project overview, supported dialects, bin/mqlc compilation guidance, a high-level list of major framework subsystems, configuration precedence (global -> terminal -> account), and contributor recommendations to preserve legacy lifecycle hooks.
• Reformat and reorganize existing README content and add a direct pointer to CODEBASE_ANALYSIS.md for deep-dive architecture documentation.

Testing

• No automated tests were added or modified because this change only affects documentation files.
• Repository CI configuration was not changed by this PR and no CI runs were triggered as part of this rollout.
• Please run the existing automated CI (e.g., GitHub Actions) as usual to validate repository checks if desired.

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Codex Task