add demo sources: VHS tapes, helper scripts, and tutorial

Tracks the inputs that drive `mage demo` so the GIFs and screenshots
under demo/assets/ can be reproduced from a checkout. The generated
assets themselves (~50 MB of GIFs and PNGs) are excluded via gitignore
since they're fully reproducible from the tapes in ~10 min.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/demo/scripts/sudo-keepalive.sh b/demo/scripts/sudo-keepalive.sh
new file mode 100755
index 0000000..4ae1e27
--- /dev/null
+++ b/demo/scripts/sudo-keepalive.sh
@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+# Refreshes the sudo timestamp every minute so a long demo regen never trips a
+# password prompt. Intended to be backgrounded by `mage demo` and killed at the
+# end of the run.
+
+set -u
+
+trap 'exit 0' TERM INT
+
+while true; do
+    sudo -n true 2>/dev/null || exit 1
+    sleep 60
+done