Stage 9: CI build on a self-hosted Gitea runner (0.7.0)

- .gitea/workflows/build.yml builds the packages and both ISOs with
  `make iso iso-server` on pushes to main and dev, v* tags and on demand
- ci/runner: setup of the CI host (WSL2 Ubuntu 24.04 with Docker Engine
  and gitea-runner as a systemd service, autostart task for Windows)
- scripts/builder.sh: DASOS_OUT keeps out/ outside the checkout, so CI
  reuses void-packages, the masterdir and the download cache
- README and TODO updated

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/builder.sh

@@ -1,18 +1,21 @@
 #!/usr/bin/env bash
 # Runs a command inside the Void Linux builder container.
 # The project is mounted at /work; downloaded packages are cached in out/cache/xbps.
+# DASOS_OUT puts out/ elsewhere (CI keeps it between checkouts).
 set -euo pipefail
 
 root=$(cd "$(dirname "$0")/.." && pwd)
+out=${DASOS_OUT:-$root/out}
 image=dasos-builder
 
 docker build --quiet --tag "$image" "$root/docker/builder" >/dev/null
-mkdir -p "$root/out/cache/xbps"
+mkdir -p "$out/cache/xbps"
 
 # --privileged: mklive mounts /proc, /sys, /dev and a loop device for the root image
 exec docker run --rm --privileged \
   --volume "$root:/work" \
-  --volume "$root/out/cache/xbps:/var/cache/xbps" \
+  ${DASOS_OUT:+--volume "$out:/work/out"} \
+  --volume "$out/cache/xbps:/var/cache/xbps" \
   --env HOST_UID="$(id -u)" \
   --env HOST_GID="$(id -g)" \
   "$image" "$@"