docs: add Adding an Example to CONTRIBUTING and sync the PR checklist

CONTRIBUTING sent contributors to an examples section that did not exist,
so the gates Validate and the gallery build enforce (examples/skills.json,
the 640 card) were documented only in agent-facing files. The new section
lists every step and links docs/new-example-prompt.md; the PR template's
example line now names the skills.json entry and the card. The template
layout and rule-length guidance now match what ships.

Closes #522

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LpkeXRvikhJZSVGBFM91Dv
Signed-off-by: TM Hospitality Strategies <TMHospitalityStrategies@gmail.com>

Author: TMHSDigital

.github/PULL_REQUEST_TEMPLATE.md

@@ -28,7 +28,7 @@ Merge evidence is the PR-head 5.2 + 4.5 smoke jobs (state the versions from thos
 - [ ] Explicit paths only (`git add` never `-A` / `.`). Leave unstaged Cursor-injected `CLAUDE.md` hunks.
 - [ ] Counts in `README.md` match disk if content was added or removed (`validate-counts`).
 - [ ] Manifest arrays list every new skill / rule / snippet / template / example / showcase piece (`validate-manifest`). Do not touch the `"version"` line.
-- [ ] New example: `gallery.json`, `tests/smoke/catalog.json` row, README row, hero/preview webp, `python scripts/build_gallery.py`, framing / contact-sheet gates as in `CLAUDE.md`.
+- [ ] New example: `tests/smoke/catalog.json` row with a falsifier, `examples/skills.json` entry + `python scripts/build_examples_index.py`, README count. Rendered examples also: `gallery.json` entry with `alt`, hero + `-hero-640.webp` card + preview webp, `python scripts/build_gallery.py`, framing / contact-sheet gates ([CONTRIBUTING.md](../CONTRIBUTING.md#adding-an-example)).
 - [ ] Every new check was falsified once (break it, non-zero exit, restore) — or this PR has no new check.
 - [ ] DCO `Signed-off-by:` on every commit ([CONTRIBUTING.md](../CONTRIBUTING.md)).
 - [ ] No credentials, business emails, or local filesystem paths.

CONTRIBUTING.md

@@ -17,7 +17,9 @@ The fastest useful contributions are small and need no Blender run:
 Then: fork, branch, `uv sync`,
 `uv run python tests/run_all.py`, and open a PR with a DCO sign-off (`git commit -s`;
 see the end of this file). Examples and showcase pieces have more gates
-(falsifiers, exit-code tables, renders); read their sections first.
+(falsifiers, exit-code tables, renders); read
+[Adding an Example](#adding-an-example) or
+[Adding a Showcase Piece](#adding-a-showcase-piece) first.
 
 ## Getting Started
 
@@ -64,10 +66,12 @@ rules/
 snippets/
   <snippet-name>.py
 templates/
-  <template-name>/
+  extension-addon-template/        # an add-on: manifest + package
     blender_manifest.toml
     __init__.py
     README.md
+  headless-batch-script-template/  # a script: script.py + README.md
+  ai-asset-pipeline-template/      # a script: pipeline.py + README.md
 examples/
   gallery.json
   <example-name>/
@@ -127,7 +131,7 @@ showcase/
    too narrow means the rule silently stops firing, which is worse than
    over-applying. Record the scope in the `CLAUDE.md` rules table to match.
 
-3. Write 30 to 80 lines: the anti-pattern, a code example showing it wrong, a code example showing it right, and a short "Why it matters" section.
+3. Keep it focused (the shipped rules run about 70 to 170 lines): the anti-pattern, a code example showing it wrong, a code example showing it right, and a short "Why it matters" section.
 
 ## Adding a Snippet
 
@@ -140,6 +144,34 @@ showcase/
 1. Add a directory under `templates/`, e.g. `templates/headless-batch-script-template/`.
 2. Include all files needed for an immediate copy-paste starting point. For add-on templates, include `blender_manifest.toml`, `__init__.py`, and a brief `README.md`.
 
+## Adding an Example
+
+An example is a runnable headless script that asserts one API contract and
+exits non-zero when it breaks. The full procedure, render standard and gates
+are in [`docs/new-example-prompt.md`](docs/new-example-prompt.md) and
+`CLAUDE.md` § Examples; copy the anatomy of `examples/bmesh-gear/`. Every
+example needs:
+
+1. `examples/<kebab-name>/` with the script and a README that has an exit-code
+   table (`0` pass, `1` uncaught exception, `2` argparse usage, checks from
+   `3` up) and a falsifier: a flag that breaks the contract so one named check
+   exits with its own code.
+2. A `tests/smoke/catalog.json` row with at least one falsifier
+   (`{"args": ["--your-flag"], "expect_exit": N}`). `tests/check_smoke_catalog.py`
+   rejects a row without one.
+3. An `examples/skills.json` entry naming the skills it proves, then
+   `python scripts/build_examples_index.py` (Validate fails on a missing entry).
+4. **Rendered examples only** (when the contract is visible in pixels): an
+   `examples/gallery.json` entry with an `alt` sentence, a 1280x720 hero
+   webp in `docs/gallery/assets/`, its 640x360 card `<name>-hero-640.webp`
+   (`python scripts/make_thumbs.py`; the gallery build exits 5 without it), a
+   1200x675 preview webp, the framing gate on the `--output` path, a
+   committed contact sheet, then `python scripts/build_gallery.py`.
+   `python scripts/render_hero.py --blender PATH --only NAME` writes all three
+   webps. A **check-only** example skips this step and stays out of
+   `gallery.json`.
+5. Update the README example count (`validate-counts`).
+
 ## Adding a Showcase Piece
 
 Read [`showcase/README.md`](showcase/README.md) first. Showcase asserts