docs: README quality-of-life pass — collapsible example categories, quick start, nav strip

The 20-example table was a ~300-line wall between the fold and the usage
docs. Examples now sit in five themed collapsible groups behind a visible
four-thumbnail teaser, with a nav strip, a quick-start section, a smoke-test
badge, a refreshed roadmap blurb, and a contributing section. Card copy is
unchanged except aligning the grease-pencil blurb with the corrected
frames.new(1) card. CI-enforced counts language preserved verbatim.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: TMHSDigital