The build-if-needed job (used for workflow_dispatch) was not building
the langflow-sdk package. Since lfx depends on langflow-sdk>=0.1.0
and langflow-sdk is not yet published to PyPI, all test jobs failed
during lfx installation with 'No solution found'.
Changes:
- Build langflow-sdk wheel in build-if-needed job
- Upload SDK artifact and output sdk-artifact-name
- Update SDK download conditions with build-if-needed fallback
- Update SDK+LFX combined/individual install conditions to properly
route through the combined installer when both are available