ci: revert to Docker image build + registry push (no deploy)

Drop the LXC deploy step. Pipeline now stops at publishing the image
to the Gitea registry; deployment is handled out of band.

Restored:
- Dockerfile (multi-stage: curl-builder + quarkus-micro-image:2.0,
  generic via build-output/*-runner wildcard, COPY --chown=1001:1001)
- compose.yaml (one-shot install of the published image)
- .dockerignore (excludes build-output/)

CI workflow:
- Installs docker-buildx (needed for COPY --chown)
- Uses docker buildx build
- chmod 775 and echo securerandom happen in the 'Stage binary for Docker'
  step; the final image has no RUN commands
- Tags :latest and :<short-sha>, pushes with retry

No deploy step. Pull the image with docker compose / run it manually.

compose.yaml

@@ -0,0 +1,25 @@
+services:
+  shot-crafter:
+    image: gitea.danielarroyo.cl/proyectos/shot-crafter-calculator:latest
+    container_name: shot-crafter
+    restart: unless-stopped
+    ports:
+      - "8080:8080"
+    environment:
+      QUARKUS_HTTP_HOST: 0.0.0.0
+      QUARKUS_HTTP_PORT: 8080
+      QUARKUS_DATASOURCE_JDBC_URL: jdbc:h2:file:/work/data/shots;DB_CLOSE_DELAY=-1
+      APP_AUTH_COOKIE_SECURE: "false"
+      APP_AUTH_COOKIE_NAME: auth-token
+    volumes:
+      - shot-crafter-data:/work/data
+    healthcheck:
+      test: ["CMD", "curl", "-fsS", "--max-time", "5", "http://localhost:8080/q/health/live"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 30s
+
+volumes:
+  shot-crafter-data:
+    name: shot-crafter-data