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)

Start with server/verification-request/schemas/verification-request.schema.ts, then trace every verification-request service and controller query and identify the listing queries targeted by the index. Review the migration path for existing documents. Done means namespace defaults to main, existing documents are backfilled, all query points are namespace-filtered, and the compound indexes support listing queries.

索引モデルが issue の本文から書いたものです。