Force-recreate containers on deploy and verify the served build

The frontend container was serving the very first build (498-byte index.html)
through every later deploy: `docker compose up -d` did not replace a
config-identical service. Deploy now uses `build --pull` and
`up --force-recreate`, the frontend image writes a .build-version marker, and
the workflow fails the deploy if the served marker != the commit SHA.

.gitea/workflows/deploy.yml

@@ -178,14 +178,19 @@ jobs:
           done
           built=0
           for i in 1 2 3 4 5; do
-            if docker compose build; then built=1; break; fi
+            # --pull refreshes base images; the build args carry the new commit
+            # so the cache is invalidated per release.
+            if docker compose build --pull; then built=1; break; fi
             echo "docker compose build failed (attempt $i); retrying in 30s"
             sleep 30
           done
           [ "$built" = "1" ] || { echo "::error::compose build failed after retries"; exit 1; }
-          # Bring the new stack up and wait for healthchecks. No pre-`down`, so
-          # the old containers keep serving until the new ones are healthy.
-          if ! docker compose up -d --remove-orphans --wait --wait-timeout 300; then
+          # --force-recreate guarantees the containers are replaced with the
+          # freshly built images. Without it a config-identical service can be
+          # left running the previous image (stale UI after a deploy).
+          # No pre-`down`, so the old containers keep serving until the new ones
+          # are healthy.
+          if ! docker compose up -d --remove-orphans --force-recreate --wait --wait-timeout 300; then
             echo "::error::New stack is unhealthy; rolling back to previous images"
             docker compose down --remove-orphans || true
             for img in crypto_trading-backend crypto_trading-frontend; do
@@ -193,7 +198,7 @@ jobs:
                 docker tag "${img}:prev" "$img"
               fi
             done
-            docker compose up -d --remove-orphans --wait --wait-timeout 300 || true
+            docker compose up -d --remove-orphans --force-recreate --wait --wait-timeout 300 || true
             exit 1
           fi
 
@@ -202,6 +207,19 @@ jobs:
           docker compose ps
           docker compose logs --tail=80
 
+      - name: Verify the deployed frontend matches this commit
+        run: |
+          # The container must serve the build stamped with this commit's SHA.
+          # Without this, a config-identical service could keep an old image and
+          # serve a stale UI even though the deploy "succeeded".
+          want="${CRYPTO_BUILD_VERSION:-unknown}"
+          got="$(docker compose exec -T frontend cat /usr/share/nginx/html/.build-version 2>/dev/null | tr -d '[:space:]' || true)"
+          echo "expected=${want} served=${got:-<missing>}"
+          if [ "$want" != "unknown" ] && [ "$got" != "$want" ]; then
+            echo "::error::frontend container is serving a stale build; failing deploy"
+            exit 1
+          fi
+
       - name: Health check (HTTP)
         run: |
           probe_backend() {