docs: starter stacks in the site README and contributing guide

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wc67NX9MM964uaVGn4bpZJ

Author: TMHSDigital

CONTRIBUTING.md

@@ -36,6 +36,8 @@ One new markdown file is enough — the website rebuilds from frontmatter on dep
 11. Add a row to the matching category `README.md`. This is required: the validator fails an entry that is not listed there, and the row's licence cell must match your frontmatter.
 12. Optional: add the `id` to `site/config.json` → `featured` to pin it under Safe starting points.
 
+To add a starter stack (one pick per need for a kind of game), follow [`stacks/README.md`](stacks/README.md).
+
 ### Frontmatter rules
 
 - `license`: the source's licence, written as one of the values in [`site/license-vocabulary.json`](site/license-vocabulary.json) (e.g. `CC0`, `CC-BY-3.0`, `SIL OFL`, `GPL-3.0-or-later`, `custom`, `varies`). If the source uses a licence the vocabulary lacks, add it there first, with its SPDX mapping and attribution class. For GPL, record `-only` or `-or-later` only when the project itself says which; otherwise use the bare `GPL-2.0` or `GPL-3.0`.

site/README.md

@@ -13,6 +13,7 @@ Static GitHub Pages UI for this catalog.
 | `site/config.json` → `categories` / `guides` | Labels and guide links |
 | `site/public/*` | Page chrome / design |
 | An entry's body (Notes, Evidence) | Its page at `entry/<id>/` |
+| `stacks/<id>.md` | Its page at `stack/<id>/`, the homepage Starter stacks list, and "Used in" on each picked entry |
 
 ## Public JSON
 
@@ -46,6 +47,15 @@ The build also writes `llms.txt` (one line per entry) and `llms-full.txt` (with
 entry's Notes) for AI assistants, and checks every generated page before it succeeds.
 Tests: `node site/lib/lib.test.mjs`.
 
+## Starter stacks
+
+`build.mjs` writes `stack/<id>/index.html` for each file in `stacks/` (the format is in
+`stacks/README.md`). The page's "What this stack owes" panel is computed from the picked
+entries: credit lines to ship, picks that need no credit, aggregators to check file by
+file, and open questions. A stack never states a licence itself. V15 in `checks.mjs`
+fails a stack whose pick is missing, deprecated or malformed, or whose why sentence
+names a licence; `validate.mjs` and `build.mjs` both run it.
+
 ## Social preview
 
 `docs/images/readme/og-card.png` is a 1200x630 screenshot of this site's first screen.