Lowercase the GHCR image name in the build workflow (#2)

\${{ github.repository }} returns the canonical mixed-case
'epiphanyplx/Secret-Lair-Monitor', but Docker tag validation rejects
uppercase characters, so 'docker buildx build --tag
ghcr.io/epiphanyplx/Secret-Lair-Monitor:latest' fails immediately with
"repository name must be lowercase" and the workflow never publishes.
Add a step that lowercases the name into IMAGE_NAME_LC before use so the
push goes to ghcr.io/epiphanyplx/secret-lair-monitor — matching what
docker-compose.yml already references.

Co-authored-by: Claude <noreply@anthropic.com>

Author: epiphanyplx

.github/workflows/build.yml

@@ -18,6 +18,9 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Compute lowercase image name
+        run: echo "IMAGE_NAME_LC=$(echo '${{ env.IMAGE_NAME }}' | tr '[:upper:]' '[:lower:]')" >> "$GITHUB_ENV"
+
       - uses: docker/login-action@v3
         with:
           registry: ${{ env.REGISTRY }}
@@ -29,5 +32,5 @@ jobs:
           context: .
           push: true
           tags: |
-            ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:latest
-            ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:${{ github.sha }}
+            ${{ env.REGISTRY }}/${{ env.IMAGE_NAME_LC }}:latest
+            ${{ env.REGISTRY }}/${{ env.IMAGE_NAME_LC }}:${{ github.sha }}