Add a README First 60 seconds hero section (before/after + outcome bullets)

[ivklgn]

Problem

README.md jumps from the tagline straight to the Commands table. There is no above-the-fold "First 60 seconds" section, no before/after diagram and no outcome bullets, so a first-time visitor cannot quickly grasp what changes after install — a likely contributor to install bounce.

Expected result

A tight (<20-line) "First 60 seconds" block at the very top of the README:

• a two-column before/after Mermaid flowchart (flat ad-hoc markdown pile → typed, related graph), and
• three short outcome bullets naming the first-session deltas,
  with the existing "what it does" narrative reordered below it.

Impact

Communicates value in the first screenful, reducing bounce and raising the odds a visitor installs or contributes. Pure-markdown change with no external assets — a good first contribution.

Proposed approach

• Add the before/after Mermaid diagram + three outcome bullets at the top.
• Reorder the existing narrative below the hero.

Acceptance criteria

• The README opens with the "First 60 seconds" hero; the diagram renders on GitHub.

References

Design rationale: .archcore/plugin/readme-first-60-seconds.idea.md (status: draft). Code: README.md.