feat: FCM 사용자별 타겟 알림 발송 기능 추가

- today_issues 테이블에 target_user_id 컬럼 추가 (마이그레이션)
- TodayIssue 모델: target_user_id 필드, targetUser 관계, forUser/targetedTo 스코프 추가
- TodayIssue 모델: 기안 상태 뱃지 상수 추가 (BADGE_DRAFT_APPROVED/REJECTED/COMPLETED)
- TodayIssueObserverService: createIssueWithFcm, sendFcmNotification, getEnabledUserTokens에 targetUserId 파라미터 추가
- TodayIssueObserverService: handleApprovalStepChange - 결재자에게만 발송
- TodayIssueObserverService: handleApprovalStatusChange 추가 - 기안자에게만 발송
- ApprovalIssueObserver 신규 생성 및 AppServiceProvider에 등록
- i18n: 기안 승인/반려/완료 알림 메시지 추가

결재요청은 결재자(ApprovalStep.user_id)에게만,
기안 승인/반려는 기안자(Approval.drafter_id)에게만 FCM 발송

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/Providers/AppServiceProvider.php

@@ -8,6 +8,7 @@
 use App\Models\Members\User;
 use App\Models\Orders\Client;
 use App\Models\Orders\Order;
+use App\Models\Tenants\Approval;
 use App\Models\Tenants\ApprovalStep;
 use App\Models\Tenants\Bill;
 use App\Models\Tenants\Deposit;
@@ -21,6 +22,7 @@
 use App\Observers\ExpenseSync\WithdrawalExpenseSyncObserver;
 use App\Observers\MenuObserver;
 use App\Observers\TenantObserver;
+use App\Observers\TodayIssue\ApprovalIssueObserver;
 use App\Observers\TodayIssue\ApprovalStepIssueObserver;
 use App\Observers\TodayIssue\BadDebtIssueObserver;
 use App\Observers\TodayIssue\ClientIssueObserver;
@@ -85,6 +87,7 @@ public function boot(): void
         Stock::observe(StockIssueObserver::class);
         ExpectedExpense::observe(ExpectedExpenseIssueObserver::class);
         ApprovalStep::observe(ApprovalStepIssueObserver::class);
+        Approval::observe(ApprovalIssueObserver::class);
         Client::observe(ClientIssueObserver::class);
         Deposit::observe(DepositIssueObserver::class);
         Withdrawal::observe(WithdrawalIssueObserver::class);