B2B-2 · Namespace-scope verification-requests (schema + queries + backfill)

Part of the B2B epic (Fase 1 · item 1.1b). Verification requests are client data (unlike personalities, which stay global by decision) — today the schema has **no `nameSpace` field at all**.

## What
- [ ] Add `nameSpace` to `server/verification-request/schemas/verification-request.schema.ts` (default `main`)
- [ ] Filter every query point in `verification-request` service/controller by namespace
- [ ] Backfill migration (existing docs → `main`)
- [ ] Compound index `(nameSpace, …)` for the listing queries

**Effort:** ~1 SP · **Depends on:** — (parallel with B2B-1)