ci: Replace GitLab CI with Gitea Actions workflow

Switched from GitLab CI to Gitea Actions for container builds.
Triggers on version tags, pushes to Gitea Container Registry.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitea/workflows/build-container.yml

@@ -0,0 +1,45 @@
+# Gitea Actions workflow for StarPunk
+# Builds and pushes container images on version tags
+
+name: Build Container
+
+on:
+  push:
+    tags:
+      - 'v[0-9]+.[0-9]+.[0-9]+'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Extract registry URL
+        id: registry
+        run: |
+          # Extract hostname from server URL (remove protocol)
+          REGISTRY_URL=$(echo "${{ github.server_url }}" | sed 's|https://||' | sed 's|http://||')
+          echo "url=${REGISTRY_URL}" >> $GITHUB_OUTPUT
+
+      - name: Login to Gitea Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ steps.registry.outputs.url }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: ./Containerfile
+          push: true
+          tags: |
+            ${{ steps.registry.outputs.url }}/${{ github.repository }}:${{ github.ref_name }}
+            ${{ steps.registry.outputs.url }}/${{ github.repository }}:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max

.gitlab-ci.yml

@@ -1,40 +0,0 @@
-# GitLab CI/CD Pipeline for StarPunk
-# Builds and pushes container images on version tags
-
-stages:
-  - build
-
-variables:
-  # Required for Docker-in-Docker
-  DOCKER_TLS_CERTDIR: "/certs"
-  # Use overlay2 driver for better performance
-  DOCKER_DRIVER: overlay2
-
-# Build and push container image
-build-container:
-  stage: build
-  image: docker:24
-  services:
-    - docker:24-dind
-  # Only trigger on version tags (e.g., v0.9.5, v1.0.0)
-  rules:
-    - if: $CI_COMMIT_TAG =~ /^v[0-9]+\.[0-9]+\.[0-9]+$/
-  before_script:
-    # Login to GitLab Container Registry
-    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
-  script:
-    # Build the container image with both version and latest tags
-    - |
-      docker build \
-        --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG \
-        --tag $CI_REGISTRY_IMAGE:latest \
-        --file Containerfile \
-        .
-    # Push both tags to the registry
-    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG
-    - docker push $CI_REGISTRY_IMAGE:latest
-  # Cache Docker layers between builds
-  cache:
-    key: docker-$CI_COMMIT_REF_SLUG
-    paths:
-      - .docker-cache