feat: complete person identity matching system with fuzzy detection, revert, and manual link

Implements the full identity matching engine: email matching (HIGH confidence),
fuzzy name matching with Levenshtein distance (MEDIUM confidence, upgradable to
HIGH with DOB tiebreaker), manual link/unlink, revert confirmed matches, and
automatic detection via PersonObserver. Includes 33 comprehensive tests, frontend
integration with confirm/dismiss/unlink UI, and match indicators in the persons list.

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

api/app/Observers/PersonObserver.php

@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Observers;
+
+use App\Models\Person;
+use App\Services\PersonIdentityService;
+
+final class PersonObserver
+{
+    public function __construct(
+        private readonly PersonIdentityService $identityService,
+    ) {}
+
+    public function created(Person $person): void
+    {
+        if ($person->user_id === null && ($person->email || $person->first_name)) {
+            $this->identityService->detectMatches($person);
+        }
+    }
+
+    public function updated(Person $person): void
+    {
+        if ($person->wasChanged('email') && $person->user_id === null && $person->email) {
+            $this->identityService->detectMatches($person);
+        }
+    }
+}