Add session-mode code generation that produces a reusable WorkflowSession class
instead of a simple oneshot script. The session mode generates code with an
in-class run/close lifecycle for warm ComfyUI reuse.
Also refactors render.py to extract shared code sections into common methods,
reducing duplication between oneshot and session renderers.
Adds WorkflowSessionRuntime with cleanup policies (per_run, session, manual)
and reset_every_n_runs support, plus 72 new tests covering session rendering,
runtime session, and session export pipeline.
Split the previous monolithic implementation into focused modules for CLI handling, workflow loading, runtime bootstrap, load ordering, planning, rendering, and file I/O. Keep the public compatibility surface intact by preserving the legacy top-level wrapper while adding as the documented entrypoint. This reduces cross-cutting coupling inside the exporter and makes the runtime/bootstrap behavior easier to evolve without carrying unrelated concerns in one file.