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>

ci/runner/config.yaml

@@ -0,0 +1,23 @@
+# gitea-runner configuration for the Das OS CI host (WSL2 distro "dasci").
+# Jobs run directly on the host: scripts/builder.sh needs the host's Docker
+# and paths it can bind-mount into the privileged Void builder container.
+log:
+  level: info
+
+runner:
+  file: /var/lib/gitea-runner/.runner
+  # One build at a time: packages and ISOs share the cache in DASOS_OUT
+  capacity: 1
+  # Matches Gitea's default job timeout; the first build bootstraps void-packages
+  timeout: 3h
+  envs:
+    DASOS_OUT: /var/lib/dasos-ci/out
+  labels:
+    - "dasci:host"
+
+cache:
+  # Build caches live in DASOS_OUT, the workflow does not use actions/cache
+  enabled: false
+
+host:
+  workdir_parent: /var/lib/gitea-runner/work