Add Gitea CI/CD workflows for automated Docker builds

Implements automated Docker image building and publishing to registry:

- build.yml: Main workflow that builds and pushes Docker images to registry
  - Triggers on push to master branch
  - Only builds when image with current version doesn't exist
  - Uses Docker BuildKit with layer caching for faster builds
  - Tags images with both version number and 'latest'

- check_image_version.yml: Reusable workflow to verify image existence
  - Reads version from package.json
  - Uses lightweight manifest inspection (no image download)
  - Returns image_exists and version as outputs

- check_package_version.yml: Reusable workflow to detect version changes
  - Compares version between commits
  - Handles edge cases (first commit, missing package.json)
  - Includes validation for version extraction failures

All workflows include proper error handling and clear logging.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitea/workflows/check_image_version.yml

@@ -0,0 +1,94 @@
+name: Check Image Version
+
+on:
+  workflow_call:
+    inputs:
+      workspacePath:
+        description: 'Path relative to repo root where package.json is located'
+        required: false
+        type: string
+        default: '.'
+      imageName:
+        description: 'Docker image name without registry FQDN or username'
+        required: true
+        type: string
+      registryUrl:
+        description: 'Docker registry URL (e.g., registry.budakova.org)'
+        required: false
+        type: string
+        default: 'registry.budakova.org'
+      registryUsername:
+        description: 'Docker registry username'
+        required: true
+        type: string
+      registryNamespace:
+        description: 'Docker registry namespace/organization (e.g., knee-cola)'
+        required: true
+        type: string
+    secrets:
+      registryToken:
+        description: 'Registry access token'
+        required: true
+    outputs:
+      image_exists:
+        description: 'Whether the image exists in the registry'
+        value: ${{ jobs.check_image.outputs.image_exists }}
+      version:
+        description: 'Current version from package.json'
+        value: ${{ jobs.check_image.outputs.version }}
+
+jobs:
+  check_image:
+    runs-on: ubuntu-latest
+    outputs:
+      image_exists: ${{ steps.manifest-check.outputs.image_exists }}
+      version: ${{ steps.version-read.outputs.version }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Read version from package.json
+        id: version-read
+        run: |
+          WORKSPACE_PATH="${{ inputs.workspacePath }}"
+          # Clean up path - remove trailing slash if present
+          WORKSPACE_PATH="${WORKSPACE_PATH%/}"
+          # Handle root directory case
+          if [ "$WORKSPACE_PATH" = "." ]; then
+            PACKAGE_JSON_PATH="package.json"
+          else
+            PACKAGE_JSON_PATH="${WORKSPACE_PATH}/package.json"
+          fi
+
+          VERSION=$(node -p "try { require('./${PACKAGE_JSON_PATH}').version } catch(e) { console.error('Error reading version:', e.message); process.exit(1) }") || {
+            echo "Error: Failed to read version from ${PACKAGE_JSON_PATH}"
+            exit 1
+          }
+          echo "version=$VERSION" >> $GITHUB_OUTPUT
+          echo "Checking for image version: $VERSION"
+
+      - name: Login to Registry
+        run: |
+          echo "${{ secrets.registryToken }}" | docker login ${{ inputs.registryUrl }} -u "${{ inputs.registryUsername }}" --password-stdin
+
+      - name: Check if image exists in registry
+        id: manifest-check
+        run: |
+          VERSION=${{ steps.version-read.outputs.version }}
+          IMAGE="${{ inputs.registryUrl }}/${{ inputs.registryNamespace }}/${{ inputs.imageName }}:${VERSION}"
+
+          echo "Checking manifest for image: $IMAGE"
+
+          if docker manifest inspect "$IMAGE" &>/dev/null; then
+            echo "Image exists in registry"
+            echo "image_exists=true" >> $GITHUB_OUTPUT
+          else
+            echo "Image does not exist in registry"
+            echo "image_exists=false" >> $GITHUB_OUTPUT
+          fi
+
+      - name: Summary
+        run: |
+          echo "Version: ${{ steps.version-read.outputs.version }}"
+          echo "Image exists: ${{ steps.manifest-check.outputs.image_exists }}"