Train a Soul Character — a personalized model on a person's face that
Higgsfield uses for identity-faithful image and video generation.
Use when: "create my Soul", "train my face", "make my digital twin",
"build me an avatar", "learn my appearance", "create a character of me",
"set up identity for video", "I want my face in generated images".
Chain: train Soul (one-time, returns reference_id) → use in
higgsfield-generate via `--soul-id <id>` with models like
`text2image_soul_v2` or `soul_cinema_studio`.
NOT for: one-shot face swaps (use higgsfield-generate with --image),
named-character / non-photo avatars (use higgsfield-generate with prompt).
