feat: [finance] 계정과목 및 일반전표 API 추가

- AccountCode 모델/서비스/컨트롤러 구현
- JournalEntry, JournalEntryLine 모델 구현
- GeneralJournalEntry 서비스/컨트롤러 구현
- FormRequest 검증 클래스 추가
- finance 라우트 등록
- i18n 메시지 키 추가 (message.php, error.php)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Models/Tenants/JournalEntry.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace App\Models\Tenants;
+
+use App\Traits\BelongsToTenant;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+use Illuminate\Database\Eloquent\SoftDeletes;
+
+class JournalEntry extends Model
+{
+    use BelongsToTenant, SoftDeletes;
+
+    protected $fillable = [
+        'tenant_id',
+        'entry_no',
+        'entry_date',
+        'entry_type',
+        'description',
+        'total_debit',
+        'total_credit',
+        'status',
+        'source_type',
+        'source_key',
+        'created_by_name',
+        'attachment_note',
+    ];
+
+    protected $casts = [
+        'entry_date' => 'date',
+        'total_debit' => 'integer',
+        'total_credit' => 'integer',
+    ];
+
+    // Status
+    public const STATUS_DRAFT = 'draft';
+    public const STATUS_CONFIRMED = 'confirmed';
+
+    // Source type
+    public const SOURCE_MANUAL = 'manual';
+    public const SOURCE_BANK_TRANSACTION = 'bank_transaction';
+
+    // Entry type
+    public const TYPE_GENERAL = 'general';
+
+    /**
+     * 분개 행 관계
+     */
+    public function lines(): HasMany
+    {
+        return $this->hasMany(JournalEntryLine::class)->orderBy('line_no');
+    }
+}