Rewrite repository README

[lmdixon23]

Summary

• replace the root README with a concise, evidence-first portfolio index;
• reconcile the public inventory with the committed repository and current CI matrix;
• remove the uncommitted sentiment-analysis project and public contact address;
• lead with verified RAG, GRPO, and regularized-operator results;
• distinguish production-like implementations, simulations, prototypes, and external-resource boundaries;
• preserve direct navigation to every committed featured project and the separate AI Playgrounds repository.

Validation

• exact branch boundary: one commit and one changed file;
• all relative Markdown links resolve in the checked-out repository;
• CI inventory reconciled to 10 Python projects, 6 Rust crates, and 1 Terraform configuration;
• whitespace validation passed;
• stale sentiment-analysis and contact references are absent;
• unrelated local untracked paths were not modified.

Scope

Documentation-only change. No source code, workflows, tests, or project configuration are modified.