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

docker/build-and-push.sh

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+#!/bin/bash
+# Build and push nabarr Docker image to the Gitea container registry.
+# Run this script on any machine that has Docker and can reach forge.dilain.com.
+#
+# Usage:
+#   ./docker/build-and-push.sh [TAG]
+#   TAG defaults to "latest"
+#
+# Example:
+#   ./docker/build-and-push.sh
+#   ./docker/build-and-push.sh master
+
+set -e
+
+REGISTRY="forge.dilain.com"
+IMAGE="${REGISTRY}/laurent/nabarr"
+TAG="${1:-latest}"
+
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+
+echo "==> Building ${IMAGE}:${TAG}"
+docker build \
+  --platform linux/amd64 \
+  -t "${IMAGE}:${TAG}" \
+  -f "${REPO_ROOT}/docker/Dockerfile" \
+  "${REPO_ROOT}"
+
+echo "==> Pushing ${IMAGE}:${TAG}"
+docker push "${IMAGE}:${TAG}"
+
+echo "==> Done: ${IMAGE}:${TAG}"