docs: refresh README with repository capability review

[rad1092]

Motivation

• Update the top-level documentation to reflect a repository-wide capability audit and to make the project entrypoint concise and actionable.
• Provide a clear inventory of features (CLI, preprocessing, analysis, visualization, API/UI) and what types of analyses the codebase supports.
• Clarify the project’s NLP maturity so users know which parts are rule-based versus LLM-enabled.

Description

• Replace the existing long-form setup guide with a streamlined README.md titled BitNet Tools that summarizes purpose and quick-start steps.
• Add a structured feature inventory covering CLI commands (analyze, report, multi-analyze, compare, doctor, ui, desktop), input preprocessing (csv, .xlsx, document), analysis core (summary stats, missing/value rules, geo checks), visualization/ recommendation, and API/UI surface.
• Document supported analysis coverage (data quality, descriptive stats, multi-file aggregation, before/after comparison, geo validation, document/excel normalization) and add an explicit NLP capability assessment describing strengths and limits.
• Surface input support constraints and a short test/status section with example commands and usage snippets for common flows.

Testing

• Verified CLI help output with python -m bitnet_tools.cli --help, which returned usage info successfully.
• Executed the full test suite with pytest -q, which completed successfully with 81 passed.

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Codex Task