Fixes network isolation issue in Docker builds where containers couldn't
reach external networks (PyPI, apt repos, etc).
**Problem:**
- Multi-arch buildx builds use: --driver-opt network=host ✅
- Single-arch builds were missing: --network=host ❌
- Result: Docker build containers had [Errno 101] Network unreachable
**Root Cause:**
When docker build runs without --network=host, build containers are
isolated from the host network and can't reach external services.
**Solution:**
Add --network=host flag to single-arch docker build command on line 131.
**Testing:**
This matches the configuration used successfully in multi-arch builds.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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