refactor(core) : final legacy cleanup — app is 100% modular

LST-60 (3.3). Closes the modular-monolith migration. src/Entity was already
empty; this removes the last legacy residue.

- Doctrine: drop the legacy "App" mapping (empty src/Entity). resolve_target_
  entities already targets modules only.
- MCP User tools (Reference/) -> Core/Infrastructure/Mcp/Tool; MCP Serializer
  -> Shared/Infrastructure/Mcp (33 usages repointed).
- Controllers (mark-all-read, notification unread-count, regenerate-api-token,
  user-avatar) -> Core/Infrastructure/Controller. TokenEncryptor -> Shared/
  Infrastructure/Service (11 usages). AppVersion resource+provider -> Shared.
  ContractType enum -> Core/Domain/Enum.
- src/{Entity,State,Controller,Service,Enum,ApiResource} now empty; routes,
  MCP tool names and public API unchanged.

180 tests green, mapping valid, no route regression, cs-fixer clean.
Note: final Malio visual harmonisation (subjective) left to the PO.

src/DataFixtures/AppFixtures.php

@@ -4,7 +4,6 @@ declare(strict_types=1);
 
 namespace App\DataFixtures;
 
-use App\Enum\ContractType;
 use App\Module\Absence\Domain\Entity\AbsenceBalance;
 use App\Module\Absence\Domain\Entity\AbsencePolicy;
 use App\Module\Absence\Domain\Entity\AbsenceRequest;
@@ -15,6 +14,7 @@ use App\Module\ClientPortal\Domain\Enum\ClientTicketStatus;
 use App\Module\ClientPortal\Domain\Enum\ClientTicketType;
 use App\Module\Core\Application\Rbac\RbacSeeder;
 use App\Module\Core\Domain\Entity\User;
+use App\Module\Core\Domain\Enum\ContractType;
 use App\Module\Directory\Domain\Entity\Client;
 use App\Module\Directory\Domain\Entity\Prospect;
 use App\Module\Directory\Domain\Enum\ProspectStatus;