feat(P03): Storage substrate — Stash, Vault, Root-Pool types

---ci---
project: oy
phase: 3
milestone: v0.1
status: execute
---/ci---

Phase 3 (Component 5: Storage Substrate) skeleton:
- x/stash: per-Holder sovereign storage (§5), Still flag (§10), maturity tracking (§9.1)
- x/vault: per-Stand governed storage (§5), sub-Vault allocations
- x/rootpool: mesh treasury (§5), attested by Watchers, visible to all Holders
- 4 unit tests passing (Freeholder maturity thresholds verified: 90d, 30d max gap)
- Lexicon compliant

x/vault/types/types.go

@@ -0,0 +1,42 @@
+package types
+
+import "encoding/json"
+
+const (
+	ModuleName   = "vault"
+	StoreKey     = ModuleName
+	RouterKey    = ModuleName
+	QuerierRoute = ModuleName
+)
+
+// Vault is a per-Stand governed storage (§5)
+// Governed by the Stand Council (§19). Holds shared funds for a Stand.
+type Vault struct {
+	VaultID      string `json:"vault_id" yaml:"vault_id"`
+	StandID      string `json:"stand_id" yaml:"stand_id"`
+	CreatedAt    int64  `json:"created_at" yaml:"created_at"`
+	BalanceGrain int64  `json:"balance_grain" yaml:"balance_grain"`
+}
+
+// VaultAllocation tracks sub-Vault allocations within a Stand
+type VaultAllocation struct {
+	VaultID    string `json:"vault_id" yaml:"vault_id"`
+	SubVaultID string `json:"sub_vault_id" yaml:"sub_vault_id"`
+	Percentage uint32 `json:"percentage" yaml:"percentage"`
+	Purpose    string `json:"purpose" yaml:"purpose"`
+}
+
+type Params struct{}
+
+func DefaultParams() Params { return Params{} }
+
+type GenesisState struct {
+	Params Params  `json:"params" yaml:"params"`
+	Vaults []Vault `json:"vaults" yaml:"vaults"`
+}
+
+func DefaultGenesisState() *GenesisState {
+	return &GenesisState{Params: DefaultParams(), Vaults: []Vault{}}
+}
+
+func ValidateGenesis(bz json.RawMessage) error { return nil }