feat: module architecture improvements — session keys, dependency graph, event dispatcher, deactivation hooks

Six targeted improvements to the modular monolith platform:

1. Fix AddressBook session key prefix to follow module.<id>.* convention
2. Move ADDRESS_BOOK_VIEW permission constant from core PermissionService into module
3. Add declarative JSON schema for module manifests (.agents/contracts/)
4. Add `requires` field with missing-dependency and circular-dependency detection
5. Add lightweight fire-and-forget event dispatcher (user.created/deleted/login/logout)
6. Add module deactivation hook interface and CLI script (bin/module-deactivate.php)

Includes 15 new architecture/unit tests covering all new functionality.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/Unit/Module/AddressBookAuthorizationPolicyTest.php

@@ -38,7 +38,7 @@ final class AddressBookAuthorizationPolicyTest extends TestCase
     public function testAllowedWithPermission(): void
     {
         $permissionService = $this->permissionGatewayAllowing([
-            5 => [PermissionService::ADDRESS_BOOK_VIEW],
+            5 => [AddressBookAuthorizationPolicy::PERMISSION_KEY],
         ]);
 
         $policy = new AddressBookAuthorizationPolicy($permissionService);