docs(readme): replace the 1,300-line catalog with a featured strip and the gallery

README was 1,541 lines, ~88% of it a showcase thumbnail grid and a
per-example catalog that duplicated the live gallery (which has filters,
full-size renders and each README). Usage, versions and license sat past
line 1,450.

- "Showcase" and "Examples" become one "Examples and showcase" section: what
  each is, where it lives, a link to the gallery, and a featured strip of
  four example and four showcase previews. Per-example prose already lives in
  each examples/<name>/README.md and on its gallery page.
- "How content is organized" now lists examples/, showcase/ and claude/.
- README is 218 lines; every aggregate count stays, so check_counts passes.
- tests/check_counts.py drops its exclusion for the per-category <details>
  summaries, which no longer exist.
- CLAUDE.md and docs/new-example-prompt.md no longer list "a README gallery
  row" as an example wiring step.

Closes #338

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: TMHSDigital

CLAUDE.md

@@ -124,7 +124,7 @@ example still carries a `tests/smoke/catalog.json` row and a falsifier.
 gallery's source of truth. When authoring a new gallery example, copy the anatomy of
 `examples/bmesh-gear/` (script structure, README shape, dark-studio render recipe) and
 wire all of: gallery.json entry (with an `alt` sentence describing the still; the build fails without one), `.cursor-plugin/plugin.json` examples array (CI-gated),
-a `tests/smoke/catalog.json` row, a README gallery row, hero webp (1280×720) in
+a `tests/smoke/catalog.json` row, hero webp (1280×720) in
 `docs/gallery/assets/` + its 640×360 card variant `<name>-hero-640.webp` (`python scripts/make_thumbs.py`; the gallery build exits 5 without it) + preview webp (1200×675), then run `python scripts/build_gallery.py`.
 A check-only example wires only the `.cursor-plugin/plugin.json` entry, the
 `tests/smoke/catalog.json` row, and its README — it is deliberately absent from