Add update-demo script for quarto-demo subtree

Shell script wraps the git subtree pull command so the long
prefix path and remote URL don't need to be remembered.

Author: cderv

tools/screenshots/CLAUDE.md

@@ -44,6 +44,7 @@ Use `/screenshot` to walk through the process:
 | `npm run render` | Render example Quarto projects |
 | `npm run serve` | Serve rendered sites locally |
 | `npm run compress` | Compress PNGs with oxipng |
+| `npm run update-demo` | Pull latest quarto-demo subtree from upstream |
 | `npm run help` | Show available commands |
 
 ## Manifest
@@ -224,6 +225,17 @@ Both can be combined. `cropBottom` is applied first, then `maxHeight`.
 - CI compresses all changed PNGs after merge (safety net)
 - `npm run capture` compresses by default (`--no-compress` to skip, or `defaults.compress: false` in manifest)
 
+## Example Site (quarto-demo subtree)
+
+`examples/quarto-demo/` is a git subtree of
+[quarto-dev/quarto-demo](https://github.com/quarto-dev/quarto-demo). To pull
+upstream changes:
+
+    npm run update-demo
+
+This runs `git subtree pull --squash` from the repo root. Extra args are passed
+through (e.g., `npm run update-demo -- --message "Update demo site"`).
+
 ## Environment
 
 - `package.json` lives in `tools/screenshots/` — run `npm` commands from that directory

tools/screenshots/package.json

@@ -9,7 +9,8 @@
     "compress": "node scripts/compress.js",
     "capture": "node capture.js",
     "open": "node scripts/open.js",
-    "validate": "node scripts/validate.js"
+    "validate": "node scripts/validate.js",
+    "update-demo": "bash scripts/update-demo.sh"
   },
   "dependencies": {
     "ajv": "^8.18.0",

tools/screenshots/scripts/update-demo.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+# Update the quarto-demo git subtree from upstream.
+# Run from anywhere inside the repo.
+
+set -euo pipefail
+
+REPO_ROOT="$(git rev-parse --show-toplevel)"
+PREFIX="tools/screenshots/examples/quarto-demo"
+REMOTE="https://github.com/quarto-dev/quarto-demo"
+BRANCH="main"
+
+cd "$REPO_ROOT"
+git subtree pull --prefix="$PREFIX" "$REMOTE" "$BRANCH" --squash "$@"