Remove Docker build from CI, add local push-docker.sh script

crane can't pull scratch in CI. Docker images are built locally
on Mac where Docker is available, then pushed to Gitea registry.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/push-docker.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+# Build and push Docker image to Gitea registry.
+# Run on a machine with Docker (your Mac).
+#
+# Usage:
+#   ./scripts/push-docker.sh v0.1.0
+set -euo pipefail
+
+cd "$(dirname "$0")/.."
+
+# Load .env if present
+if [[ -f .env ]]; then
+    set -a
+    source .env
+    set +a
+fi
+
+TAG="${1:?Usage: $0 <tag>  (e.g. v0.1.0)}"
+REGISTRY="${GITEA_URL:-https://git.manko.yoga}"
+REGISTRY_HOST="${REGISTRY#https://}"
+REGISTRY_HOST="${REGISTRY_HOST#http://}"
+IMAGE="${REGISTRY_HOST}/manawenuz/btest-rs"
+
+echo "=== Building Docker image for ${IMAGE}:${TAG} ==="
+
+# Build the image
+docker build -t "${IMAGE}:${TAG}" -t "${IMAGE}:latest" .
+
+echo ""
+echo "=== Pushing to ${REGISTRY_HOST} ==="
+
+# Login if needed (uses GITEA_TOKEN from .env)
+if [[ -n "${GITEA_TOKEN:-}" ]]; then
+    echo "${GITEA_TOKEN}" | docker login "${REGISTRY_HOST}" -u token --password-stdin
+fi
+
+docker push "${IMAGE}:${TAG}"
+docker push "${IMAGE}:latest"
+
+echo ""
+echo "Done! Images pushed:"
+echo "  ${IMAGE}:${TAG}"
+echo "  ${IMAGE}:latest"
+echo ""
+echo "Run with:"
+echo "  docker run --rm -p 2000:2000 -p 2001-2100:2001-2100/udp ${IMAGE}:${TAG} -s -v"