Move version display to GET /api/health/version in HealthController

Uses GetApplicationVersion(Assembly.GetExecutingAssembly()) — the same
timestamp-based version already logged at startup and baked into the
assembly via the csproj <Version> property. Removes the minimal-API
/version endpoint from web/Program.cs and reverts the web Dockerfile
APP_VERSION build-arg (no longer needed).

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

.gitea/workflows/build.yml

@@ -47,10 +47,7 @@ jobs:
 
       - name: Build Web image
         run: |
-          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}:${IMAGE_TAG}" .
+          docker build -f web/Dockerfile -t "${REGISTRY_HOST}/${WEB_IMAGE}:${IMAGE_TAG}" .
 
       - name: Build CV cleanup job image
         run: |