feat(directory) : add Prospect entity with conversion to Client (back)

LST-58 (2.4), part 2 — Prospect (new entity). Completes the Directory backend.

- ProspectStatus enum (new/contacted/qualified/won/lost) + Prospect entity
  (name, company, email, phone, address, status, source, notes,
  convertedClient -> ClientInterface) with Timestampable/Blamable + #[Auditable].
- API: GetCollection/Get (ROLE_USER), Post/Patch/Delete (ROLE_ADMIN),
  custom POST /prospects/{id}/convert (ConvertProspectProcessor: creates a
  Client from the prospect, links convertedClient, sets status=Won; idempotent).
  SearchFilter on status.
- Repository interface + Doctrine impl (bound); 6 MCP tools (list/get/create/
  update/delete/convert-prospect); Serializer::prospect(). Module perms
  directory.prospects.view/manage. Demo fixtures (3 prospects, one converted).
- Additive migration: CREATE TABLE prospect + FKs ON DELETE SET NULL + COMMENT.

163 tests green (incl. conversion test), mapping valid, cs-fixer clean.

config/services.yaml

@@ -101,4 +101,6 @@ services:
 
     App\Module\Directory\Domain\Repository\ClientRepositoryInterface: '@App\Module\Directory\Infrastructure\Doctrine\DoctrineClientRepository'
 
+    App\Module\Directory\Domain\Repository\ProspectRepositoryInterface: '@App\Module\Directory\Infrastructure\Doctrine\DoctrineProspectRepository'
+
     App\Shared\Domain\Contract\NotifierInterface: '@App\Module\Core\Infrastructure\Notifier'