ci: pass COMMIT and DATE build args to Docker builds

ci.yml's Docker job was missing the build-args introduced alongside
the Dockerfile ARG/ldflags changes. COMMIT and DATE are now injected
into both soundtouch-service and soundtouch-web CI builds; VERSION
stays 'dev' (the Dockerfile default) since CI builds aren't tagged
releases.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -308,6 +308,10 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@d7f5e7f509e45cec5c76c4d5afdd7de93d0b3df5 # v4.1.0
 
+      - name: Set build date
+        id: build_date
+        run: echo "date=$(date -u +%Y-%m-%d)" >> $GITHUB_OUTPUT
+
       - name: Determine push eligibility
         id: push-check
         run: |
@@ -350,6 +354,9 @@ jobs:
           push: ${{ steps.push-check.outputs.should-push == 'true' }}
           tags: ${{ steps.meta-service.outputs.tags }}
           labels: ${{ steps.meta-service.outputs.labels }}
+          build-args: |
+            COMMIT=${{ github.sha }}
+            DATE=${{ steps.build_date.outputs.date }}
           cache-from: type=gha
           cache-to: type=gha,mode=max
 
@@ -373,6 +380,9 @@ jobs:
           push: ${{ steps.push-check.outputs.should-push == 'true' }}
           tags: ${{ steps.meta-web.outputs.tags }}
           labels: ${{ steps.meta-web.outputs.labels }}
+          build-args: |
+            COMMIT=${{ github.sha }}
+            DATE=${{ steps.build_date.outputs.date }}
           cache-from: type=gha
           cache-to: type=gha,mode=max