README: full slim redesign — 354 → ~200 lines, journeys told once (#27)

The page had grown by accretion across eight releases: the journeys
were explained four times (intro bullets, goals table, mermaid, three
per-journey command tables). Redesigned to the canonical slim shape:

- centered hero: h1, banner, two-line value prop, badges, mini-nav
- Install first (the #1 visitor intent), warnings folded to one callout
- ONE journeys table (goal · say · commands · you get)
- guard and GitAlive each one tight section with their visual
- family tree + sibling pattern + lazarus-github in one section
- deep dives + FAQ stay collapsed; star CTA cut to two lines
- footer carries overview/contributing/maintaining links

Cut: mermaid (duplicated the table; full version lives in OVERVIEW),
per-journey command tables, in-body ToC (mini-nav replaces it; README
is now under the gitalive rubric's ToC threshold), long star section.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: CognitiveCodeAI