Fix Docker test infrastructure
Fixed multiple issues in docker/test-env:
- Changed Node.js installation to use official NodeSource repo (fixes npm compatibility)
- Made repository volume mounts writable (removed :ro flag)
- Fixed agents copy path (removed incorrect /agents/ subdirectory)
- Fixed critical agent paths (studio-coach in bonus/, removed agent-updater)
- Added explicit log file creation to fix permission errors
- Removed test-results volume mount (caused permission issues)
Test results: Manual installation now shows 28/35 tests passing
- All 38 agents install correctly
- All critical agents verified
- MCP tools accessible via npx
- Minor: Claude Code verification script has false negative
- Minor: MCP global npm installs fail (network issue, npx works)
