feat(house): house vault module — capital, policy caps, modes, clearing API

[JaeLeex]

Summary

• Add nunchi-house: the house vault module of the hybrid AMM stack (PRD in PRD: Hybrid AMM design — house + CBC + off-chain bin manager #119). Owns vault capital accounting (free balance + per-market clearing reservations), per-vault risk policy (market allowlist, allocation cap, net-inventory cap, leverage ceiling), live/frozen/halt operating modes, and the authorized-submitter registry.
• Exposes the checked clearing API the CBC module composes: authorized_submitter, reserve_clearing_quote / release_clearing_quote, pure validate_clearing_fill, and settle_clearing_fill. Exposure caps bind only on exposure-increasing fills, so vaults can always trade back toward flat; the leverage ceiling L_max check runs against the keeper-posted oracle price at settlement.
• Signed net inventory uses an explicit sign+magnitude codec (NetInventory) rather than relying on platform signed-integer codec behavior.
• Follows the clob/perpetuals module pattern: transaction ops + ledger + db + genesis + optional rpc + deterministic tests, stability_scope!(ALPHA).

Deliberate v1 boundaries

• Balances are internal accounting units until chain wiring connects deposits/withdrawals to coins (same seam feat(clob): add spot order book module #117 took for fills).
• Withdrawals require a live vault with a flat book; margin-coverage-based partial withdrawal needs oracle wiring.
• "House" is an HLP analogue in the house-liquidity sense only — no liquidation-vault/backstop/ADL semantics (those stay in perpetuals).
• README flags the reserved vaults taxonomy entry — fold-in vs standalone is PRD open question 1.

Test plan

• cargo test -p nunchi-house (13 tests: codec, genesis, owner gates, mode gates, flat-book withdrawal, reservation caps, settlement round trip, frozen reduce-only, halt, net-inventory + leverage caps)
• cargo check --workspace --all-targets
• cargo check -p nunchi-house --no-default-features
• cargo clippy -p nunchi-house --all-targets -- -D warnings

Stacking

Base is jae/hybrid-amm-design (#119) → jae/spot-clob-module (#117). Landing order per the PRD: #117 → #119 → this → CBC. No chain wire tags allocated yet (coordinated against the final module set, perpetuals/ROADMAP.md §1).

[codecov]

Codecov Report

❌ Patch coverage is 70.95990% with 239 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
house/src/rpc.rs	0.00%	85 Missing ⚠️
house/src/ledger.rs	78.01%	53 Missing and 31 partials ⚠️
house/src/transaction.rs	65.75%	23 Missing and 2 partials ⚠️
house/src/types.rs	86.66%	3 Missing and 15 partials ⚠️
house/src/genesis.rs	76.11%	6 Missing and 10 partials ⚠️
house/src/db.rs	86.41%	10 Missing and 1 partial ⚠️

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