feat(bond,cover,standing): P4 MAB + Cover Claims Voucher + Shadow vouch

v0.7 P4 (REQ-054, REQ-055, REQ-060, REQ-063, D-080, D-089, D-090):

x/bond (Mutual Aid Bond): MAB struct (Bond anonymous embed) mirroring
GrowthBond; CouponDenom enum (CoverCall/MutualAidCredit/Bread-rejected);
MABIssuanceCeilingAnnualSurplusMultiple=3 locked const; ValidateMAB
rejects CouponDenomBread (FR-MAB-3 dual firewall); D-080 tagged streaming
(reserve_build_out); 4 handlers (IssueMAB with 3x ceiling check,
DebitMABProceeds with auto-Still on misuse, WitnessMABProceedsRelease
with Watcher quorum, WatcherAttestMAB); CoverKeeper reverse edge (D-089).

x/cover (Cover Claims Voucher + dissolution): CoverClaimsVoucher struct;
D-090(2) cold-start bond = max(10x avgCallSize, MinimumVoucherBond); 4
handlers (RegisterCoverClaimsVoucher, AdjudicateCoverCall with FR-CPCV-2
no self-adjudication, SlashCoverClaimsVoucher with cross-Pool bucket
drop, DissolveCoverPool with FR-MAB-4 waterfall Cover-Fee > MAB > Bread);
MAB holders have NO Voice (REQ-063).

x/standing (Shadow vouch): Vouch.IsShadow field; ShadowVouchWeightMultiplier
=0.5 locked const (REQ-060); GetVoucherWeight extended with isShadow param
(post-step 0.5x multiplier; all call sites updated); SlashReasonFraudulent
CoverCall const (REQ-055).

Coverage: bond/keeper 92.1%, cover/keeper 95.0%, standing/types 90.3%.
G-006/G-028 intact. go.mod/go.sum diff EMPTY. go vet clean. Lexicon green.

---ci---
project: oy
phase: 4
milestone: v0.7
status: execute
---/ci---

web/store/store.go

@@ -351,7 +351,7 @@ func (s *Store) ComputeStandingScore(reachID string) (float64, standingtypes.Sta
 	sum := 0.0
 	categories := map[string]bool{}
 	for _, r := range ratings {
-		w := standingtypes.GetVoucherWeight(false, r.Score, len(ratings))
+		w := standingtypes.GetVoucherWeight(false, r.Score, len(ratings), false)
 		sum += r.Score * w
 		categories[r.Category] = true
 	}