feat(p9): scope-ownership assert + fence routing approve/deny/listDecisions

Task T3.1: ActorResolver gains findScope (no-create) + assertOwns(principal,
resourceScopeId) → ForbiddenException on mismatch (KG-02). RouteService.approve/
deny now assertOwns on the decision's binding scope before mutating; listDecisions
is scoped to the caller. Fixes the critical cross-tenant mutation (tenant A could
approve tenant B's route). Also adds IiosScope.cellId + IiosOutboundCommand.scopeId
columns (migration tenant-isolation) + cell assignment on scope create. Test:
another tenant approving → Forbidden, decision unchanged, no scope created, empty list.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/prisma/schema.prisma

@@ -296,6 +296,7 @@ model IiosScope {
   workspaceId String?
   projectId   String?
   userScopeId String?
+  cellId      String   @default("cell-default") // P9 cell-partition hook
   createdAt   DateTime @default(now())
 
   sourceHandles IiosSourceHandle[]
@@ -707,6 +708,7 @@ model IiosOutboundCommand {
   target         String
   payload        Json
   status           String              @default("PENDING") // PENDING | SENT | FAILED | RATE_LIMITED | BLOCKED
+  scopeId          String?             // owning tenant scope (P9 tenant fencing + per-tenant quota)
   idempotencyKey   String              @unique
   providerRef      String?
   consentReceiptRef String?            // CMP consent receipt this send went out under (P9)