build: add manual build script and act_runner setup for Unraid

- docker/build-and-push.sh: build and push image to forge registry from
  any machine with Docker (run directly on Unraid terminal)
- docker/act_runner.compose.yml: Gitea act_runner setup to automate
  Docker builds via Gitea Actions on Unraid

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/act_runner.compose.yml

@@ -0,0 +1,29 @@
+version: "3"
+
+# Gitea act_runner - to be deployed on Unraid (or any Docker host).
+# Allows Gitea Actions workflows to run and build Docker images automatically.
+#
+# Setup steps:
+#   1. Copy this file to /mnt/user/appdata/act_runner/docker-compose.yml
+#   2. Register the runner to get a token:
+#        docker run --rm -it gitea/act_runner:latest \
+#          register --no-interactive \
+#          --instance http://10.111.111.4:3000 \
+#          --token <REGISTRATION_TOKEN> \
+#          --name unraid-runner \
+#          --labels ubuntu-latest:docker://node:16-bullseye
+#      (get the registration token from forge.dilain.com → Settings → Actions → Runners)
+#   3. Copy the generated .runner file into /mnt/user/appdata/act_runner/
+#   4. Start: docker compose up -d
+
+services:
+  act_runner:
+    image: gitea/act_runner:latest
+    container_name: act_runner
+    restart: unless-stopped
+    environment:
+      - DOCKER_HOST=unix:///var/run/docker.sock
+    volumes:
+      - /mnt/user/appdata/act_runner:/data
+      - /var/run/docker.sock:/var/run/docker.sock
+    working_dir: /data