Add complete ai.card Rust implementation

- Implement complete Rust API server with axum framework
- Add database abstraction supporting PostgreSQL and SQLite
- Implement comprehensive gacha system with probability calculations
- Add JWT authentication with atproto DID integration
- Create card master data system with rarities (Normal, Rare, SuperRare, Kira, Unique)
- Implement draw history tracking and collection management
- Add API endpoints for authentication, card drawing, and collection viewing
- Include database migrations for both PostgreSQL and SQLite
- Maintain full compatibility with Python API implementation
- Add comprehensive documentation and development guide

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

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

python/api/app/tests/test_gacha.py

@@ -0,0 +1,57 @@
+"""ガチャシステムのテスト"""
+import pytest
+from app.services.gacha import GachaService
+from app.models.card import CardRarity
+
+
+class TestGachaService:
+    """GachaServiceのテストクラス"""
+    
+    def test_determine_rarity_normal(self):
+        """通常ガチャのレアリティ判定テスト"""
+        rarities = []
+        for _ in range(1000):
+            rarity = GachaService._determine_rarity(is_paid=False)
+            rarities.append(rarity)
+        
+        # 大部分がNORMALであることを確認
+        normal_count = rarities.count(CardRarity.NORMAL)
+        assert normal_count > 900
+        
+    def test_determine_rarity_paid(self):
+        """課金ガチャのレアリティ判定テスト"""
+        rarities = []
+        for _ in range(1000):
+            rarity = GachaService._determine_rarity(is_paid=True)
+            rarities.append(rarity)
+        
+        # 課金ガチャの方がレアが出やすいことを確認
+        rare_count = sum(1 for r in rarities if r != CardRarity.NORMAL)
+        assert rare_count > 50  # 5%以上
+        
+    def test_card_id_selection(self):
+        """カードID選択のテスト"""
+        for rarity in CardRarity:
+            card_id = GachaService._select_card_id(rarity)
+            assert 0 <= card_id <= 15
+            
+    def test_cp_calculation(self):
+        """CP計算のテスト"""
+        # 通常カード
+        cp_normal = GachaService._calculate_cp(0, CardRarity.NORMAL)
+        assert 10 <= cp_normal <= 100
+        
+        # uniqueカード（5倍）
+        cp_unique = GachaService._calculate_cp(0, CardRarity.UNIQUE)
+        assert 50 <= cp_unique <= 500
+        
+    @pytest.mark.asyncio
+    async def test_draw_card(self):
+        """カード抽選の統合テスト"""
+        user_did = "did:plc:test123"
+        card, is_unique = await GachaService.draw_card(user_did, is_paid=False)
+        
+        assert card.owner_did == user_did
+        assert 0 <= card.id <= 15
+        assert card.cp > 0
+        assert card.status in CardRarity