README: slim to landing-page essentials; add "Design forces" section
explaining why pkg/result and pkg/logger exist (form over mechanism).
Remove stale API docs — those live in package comments.
CLAUDE.md: add "form over mechanism" design principle; update logging
rule to document NewCLI two-mode model; add v0.4.0 to recent work.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>