Add auto-incrementing version display to web UI footer

Exposes GET /version endpoint in the web container (reads APP_VERSION env var).
CI computes the version as 1.0.<git-commit-count> and passes it via --build-arg at build time.
Both index.html and cv-matcher/index.html show the version in the footer via a JS fetch.
docker-compose passes APP_VERSION through to the running container.

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

.gitea/workflows/build.yml

@@ -47,7 +47,10 @@ jobs:
 
       - name: Build Web image
         run: |
-          docker build -f web/Dockerfile -t "${REGISTRY_HOST}/${WEB_IMAGE}:${IMAGE_TAG}" .
+          APP_VERSION="1.0.$(git rev-list --count HEAD)"
+          docker build -f web/Dockerfile \
+            --build-arg APP_VERSION="${APP_VERSION}" \
+            -t "${REGISTRY_HOST}/${WEB_IMAGE}:${IMAGE_TAG}" .
 
       - name: Build CV cleanup job image
         run: |