Add three free church website starters

[puikinsh]

Adds three free church website starters.

Starter	For
Bethel	evangelical and Baptist congregations
Canterbury	Anglican, Episcopal and Catholic parishes
Threshold	church plants and multisite churches

Three designs from one project, so they share a stylesheet core and were built
and checked the same way — hence one PR rather than three.

Each is a real Eleventy project: src/_includes/base.njk is the shared layout,
one .njk per page carrying its own title and description in front matter, and
the navigation comes from src/_data/nav.json and is rendered with
aria-current on the current page.

Two notes in case they look odd on review:

• Permalinks are flat (about.html, not /about/). The templates' own
  JavaScript resolves the current nav link from the last path segment and
  fetches its configuration by a relative path, and directory URLs break both.
  It is documented in each README.
• No external requests at all — typefaces are self-hosted and subset to the
  faces used, and there is no analytics, CDN or webfont service. The build is
  Eleventy plus passthrough copy; there are no other dependencies.

The demos are the same designs served as static HTML, so the Speedlify scores
should be representative rather than flattering.