feat: person identity matching with detection, confirmation and audit trail

Implements enterprise-grade identity resolution (detect → suggest → confirm)
for Person ↔ User linking. Matches are detected automatically on person
creation and user account creation, then surfaced to organisers for explicit
confirmation or dismissal. No silent auto-linking.

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

api/app/Services/InvitationService.php

@@ -81,6 +81,8 @@ final class InvitationService
                 'password' => $password,
                 'email_verified_at' => now(),
             ]);
+
+            app(PersonIdentityService::class)->detectMatchesForUser($user);
         }
 
         $organisation = $invitation->organisation;