feat: add skills, version pinning, CI/CD, and generated-file headers

- Create skills: rego-pd-validator, usb-gadget-configfs, led-matrix-msgpack-rpc
- Update pd-audio-synthesis skill with Uno Q specifics
- Add Pd version check (min 0.54.0) to start-synth.sh
- Add DO NOT EDIT headers to generated pd patches
- Add Gitea Actions CI workflow for patch validation
- Add ConditionPathExists guards to legacy systemd services
- Add 'just ci' recipe for CI

scripts/start-synth.sh

@@ -30,6 +30,14 @@ if ! command -v pd &>/dev/null; then
     die "Pure Data not found. Install: apt install puredata"
 fi
 
+MIN_PD_VERSION="0.54.0"
+PD_VERSION=$(pd --version 2>&1 | grep -oP '[\d]+\.[\d]+-?[\d]*' | head -1 || echo "0.0.0")
+if printf '%s\n' "$MIN_PD_VERSION" "$PD_VERSION" | sort -V | head -1 | grep -q "^$MIN_PD_VERSION$"; then
+    info "Pd version $PD_VERSION (>= $MIN_PD_VERSION)"
+else
+    die "Pd version $PD_VERSION is too old. Need >= $MIN_PD_VERSION"
+fi
+
 if [ ! -f "$PATCH" ]; then
     die "Patch not found: $PATCH"
 fi