Curate post-beta research model expansion roadmap

[stefan-jansen]

Select the next model additions only after beta stability is achieved.

Acceptance criteria:

• Candidate models are grouped by library fit: latent factors, SDF/no-arbitrage, portfolio learning, options analytics, and other research directions.
• Each accepted candidate has a reference, expected input/output contract, and test/documentation requirements.
• Survey-only or low-fit papers are explicitly deferred rather than implemented by default.