PRD: Hybrid AMM design — house + CBC + off-chain bin manager

[JaeLeex]

Summary

• Add prds/2026-07-07-hybrid-amm-design.md: the hybrid AMM design decided at the 07-03 standup — Uniswap-v3-style bins layered onto the shared CLOB (reverse-Osmosis), split into two new on-chain modules (house, cbc) plus the Nunchi-run off-chain automated bin manager.
• Formula-first: bin ladder construction, uniform-price batch clearing (v1 auction form, v1.1 KKT risk-weighted form), house leverage ceiling, atomicity-gap bound, plus one fully worked ladder → CBC-batch example.
• Documents why the house path needs no TEE, the wire-tag coordination impact (two more modules in the final set, perpetuals/ROADMAP.md §1), and how the design stays robust to the on-chain vs. gossiped-book question raised in feat(clob): add spot order book module #117's review.

Stacking

• Base is jae/spot-clob-module (feat(clob): add spot order book module #117) so the design can reference the landed book types (ClobOperation, PlaceOrderParams, digest-backed MarketId/AssetId). Docs-only diff; retarget to main once feat(clob): add spot order book module #117 merges.
• Landing order stays: feat(clob): add spot order book module #117 → this PRD → house crate → cbc crate → perps interactions. Nothing here delays the devnet.

Review asks

The eight open questions at the bottom of the PRD — most load-bearing: crate split (Q1), v1 intent codec fields (Q2), allocation rule (Q3), and settlement-time policy enforcement if book placement moves off-chain (Q7).