Docs: LLM‑optimised algorithm priorities and rationale

[f-gueguen]

Summary

• Add an LLM‑focused section to README explaining why we ship long/complex algorithms and what to expect next
• Expand ROADMAP with a prioritized "LLM‑Optimised Additions" section (Aho–Corasick, Dinic, suffix automaton, Delaunay+KD‑Tree, BVH SAH, polygon clipping)
• Update PROJECT_DESCRIPTION with criteria for choosing high‑value modules
• Append a Planned (High LLM Value) block to docs/list.md for quick scanning

Validation

• Pure docs; no runtime changes
• Lint/typecheck/tests passed