fix(ci): install uv+Python in Docker image, fix ARM64 cross-compile

- Install uv and Python 3.12 for python_runner tests
- Use target-specific AARCH64_UNKNOWN_LINUX_GNU_OPENSSL_* env vars
  so host build scripts don't link against aarch64 libs
- Add shell: bash to Build step for Windows compatibility

Author: hanzo-dev

.github/Dockerfile

@@ -22,6 +22,10 @@ RUN node -v
 # Pre-install MCP test server dependencies so npx doesn't fail with missing modules
 RUN npx -y @modelcontextprotocol/server-everything@2025.9.12 --help 2>/dev/null || true
 
+# Install uv (Python package manager) and Python for runner tests
+RUN curl -LsSf https://astral.sh/uv/install.sh | sh
+RUN uv python install 3.12
+
 # Create a new directory for your app
 WORKDIR /app