ci: add build and distribution pipeline with goreleaser and Gitea Actions

- .goreleaser.yaml: cross-compile linux/windows, Docker image, Gitea releases
- .gitea/workflows/ci.yml: verify build on every push/PR
- .gitea/workflows/release.yml: goreleaser + Docker on tag push
- Dockerfile: switch to debian:bookworm-slim, install steamcmd from Valve
- Dockerfile.goreleaser: minimal image used by goreleaser dockers
- docker-compose.yml: parameterize SERVERS_DIR via env var

.gitea/workflows/release.yml

@@ -0,0 +1,30 @@
+name: Release
+on:
+  push:
+    tags:
+      - "v*"
+
+jobs:
+  goreleaser:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.25"
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+      - uses: docker/setup-qemu-action@v3
+      - uses: docker/setup-buildx-action@v3
+      - run: cd frontend && npm ci
+      - uses: goreleaser/goreleaser-action@v6
+        with:
+          version: "~> 2"
+          args: release --clean
+        env:
+          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
+          REGISTRY: ${{ gitea.server_host }}
+          REPOSITORY_OWNER: ${{ gitea.repository_owner }}