feat: 알림음 시스템 - FCM 발송 UI 타입 드롭다운 추가

- 알림 타입 선택 드롭다운 추가 (6개 타입)
- channel_id 검증 로직 추가
- sound_key 파라미터 제거

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/Http/Controllers/FcmController.php

@@ -97,10 +97,9 @@ public function sendPush(Request $request): View
             'tenant_id' => 'nullable|integer|exists:tenants,id',
             'user_id' => 'nullable|integer',
             'platform' => 'nullable|string|in:android,ios,web',
-            'channel_id' => 'nullable|string|max:50',
+            'channel_id' => 'nullable|string|in:push_default,push_urgent,push_payment,push_sales_order,push_purchase_order,push_contract',
             'type' => 'nullable|string|max:50',
             'url' => 'nullable|string|max:500',
-            'sound_key' => 'nullable|string|max:50',
         ]);
 
         // API 서버로 발송 요청
@@ -111,10 +110,9 @@ public function sendPush(Request $request): View
                 'tenant_id' => $request->get('tenant_id'),
                 'user_id' => $request->get('user_id'),
                 'platform' => $request->get('platform'),
-                'channel_id' => $request->get('channel_id'),
+                'channel_id' => $request->get('channel_id', 'push_default'),
                 'type' => $request->get('type'),
                 'url' => $request->get('url'),
-                'sound_key' => $request->get('sound_key'),
             ]),
             auth()->id()
         );