chore: audit follow-ups from plan review

Four small fixes surfaced by a side-by-side plan-vs-shipped pass:

- README.md: adds the Template Catalog section the plan called out —
  links to the live site URL, the install flows (web / file / Finder),
  and templates/CONTRIBUTING.md for authors. Placed right before the
  existing Contributing section, with a catalog-specific cross-link at
  the end of that section too.
- CLAUDE.md: adds the Template Catalog section so future agent sessions
  know the regenerator pipeline exists, how it relates to release.sh +
  wiki.sh, and what the schema-sync rule is when DashboardWidget or
  ProjectTemplateManifest change.
- scarf/scarfTests/ProjectTemplateTests.swift: fixes the stale
  ProjectTemplateExampleTemplateTests docstring still referencing
  `examples/templates/` (the example moved to `templates/awizemann/`
  in 70f7cea).
- .github/workflows/validate-template-pr.yml: untangles the self-
  contradictory Python-version comment. The validator is 3.9+
  compatible; CI uses 3.11 for faster runner caching. Same stdlib
  surface, same code paths — just clearer about why.

All tests still green: 22 Swift tests in 7 suites, 16 Python tests,
catalog check passes on the site-status-checker example.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -395,6 +395,16 @@ Signing prerequisites (one-time):
 - `scarf-notary` keychain profile registered via `xcrun notarytool store-credentials`
 - Sparkle EdDSA private key in Keychain item `https://sparkle-project.org` (back this up — without it, shipped apps can never receive updates)
 
+## Template Catalog
+
+Community-contributed Scarf project templates live under [`templates/`](templates/) in this repo and are browsable at **[awizemann.github.io/scarf/templates/](https://awizemann.github.io/scarf/templates/)** with live dashboard previews and one-click `scarf://install?url=…` links.
+
+- **Install from the web** — click "Install with Scarf" on any template's detail page; the app takes over from there.
+- **Install from a local file** — Scarf → Projects → Templates → Install from File…, or double-click any `.scarftemplate` in Finder.
+- **Author a template** — see [`templates/CONTRIBUTING.md`](templates/CONTRIBUTING.md) for the full walkthrough. Fork, drop a template under `templates/<your-github-handle>/<your-name>/`, open a PR; CI validates the bundle automatically.
+
+The catalog's site is a static HTML + vanilla JS build generated by [`tools/build-catalog.py`](tools/build-catalog.py) and driven by [`scripts/catalog.sh`](scripts/catalog.sh) (check / build / preview / publish). Appcast and main landing page are independent — updating the catalog never disturbs Sparkle.
+
 ## Contributing
 
 Contributions are welcome. Please open an issue to discuss what you'd like to change before submitting a PR.
@@ -405,6 +415,8 @@ Contributions are welcome. Please open an issue to discuss what you'd like to ch
 4. Push to the branch (`git push origin feature/my-feature`)
 5. Open a Pull Request
 
+For template submissions, see [`templates/CONTRIBUTING.md`](templates/CONTRIBUTING.md) — same flow, with a catalog-specific checklist + automated CI validation.
+
 ## Support
 
 If you find Scarf useful, consider buying me a coffee.