fix: source owner_principal_id from current organization

OwnerPrincipalIdField was reading currentClusterAtom, which no callers
ever wrote — so every form submission ended up with
owner_principal_id=null and the backend rejected non-admins with
"Only platform admin can create global ...". Pin the field to
currentOrganizationId instead (the Org the caller is acting under).
Cluster ownership is the wrong source: a cluster_access grant lets one
Org schedule on another Org's cluster, but the new resource is still
owned by the caller's Org, and the backend enforces
owner_principal_id == ctx.current_principal_id.

Also drops the dead currentClusterAtom.

src/atoms/user.ts

@@ -3,6 +3,15 @@ import { atomWithStorage } from 'jotai/utils';
 
 export const userAtom = atomWithStorage<any>('userInfo', null);
 
+// Backs the `currentOrganizationId` localStorage key. Stays null in
+// builds with no Org context (single-tenant), and is shared with any
+// extension that persists the same key so both sides stay in sync
+// without one side having to import from the other.
+export const currentOrganizationIdAtom = atomWithStorage<number | null>(
+  'currentOrganizationId',
+  null
+);
+
 export const GPUStackVersionAtom = atom<{
   version: string;
   git_commit: string;