feat: ref_img_resize ("720" / "1024" / "origin") replacing keep_ref_img_size

Match the C API change in QuantFunc 25878cc which renamed the edit-mode
ref-image option from a bool keep_ref_img_size to an int/string
ref_img_resize. Without this update the old "keep_ref_img_size" key in
options_json is silently dropped by the new C API and the engine always
falls back to the default 720-px long-side cap.

ImageList node:
  - Replace the BOOLEAN "keep_ref_img_size" widget with a dropdown
    "ref_img_resize" — choices "720" / "1024" / "origin", default "720".
  - 720 / 1024 — long-side cap (px)
  - origin     — keep original size, floor each dim to a multiple of 16
                 (vae_scale_factor * 2)

Generate node:
  - Forward the new field through options_json["ref_img_resize"].
  - Backwards-compat shim: if an old workflow JSON still carries the
    legacy keep_ref_img_size: True, map it to "1024" (matches the
    previous kKeepRefMaxSide constant). False / missing → "720".

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>