Document the attack model

The reasoning behind the product, written down: the three layers and
which one is unowned, exactly what a pool leaves public, each heuristic
with why it works and what closes it, why the score's weights are
published, and an explicit list of what Aether does not claim.

That last section matters most — a privacy tool that oversells is worse
than none, so the deposit staying public, the unimplemented statement
proofs, the local-only ledger and the unaudited contract are all stated
rather than left for a reviewer to discover.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>