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/db/base.py

@@ -0,0 +1,53 @@
+"""Database base configuration"""
+import os
+from pathlib import Path
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine, async_sessionmaker
+from app.core.config import settings
+
+# Create base class for models
+Base = declarative_base()
+
+# Ensure database directory exists
+db_path = Path.home() / ".config" / "syui" / "ai" / "card"
+db_path.mkdir(parents=True, exist_ok=True)
+
+# Select database URL based on configuration
+database_url = settings.database_url_supabase if settings.use_supabase else settings.database_url
+
+# Expand ~ in database URL
+if database_url.startswith("sqlite"):
+    database_url = database_url.replace("~", str(Path.home()))
+
+# Create async engine (SQLite-optimized settings)
+if "sqlite" in database_url:
+    engine = create_async_engine(
+        database_url,
+        echo=settings.debug,
+        future=True,
+        # SQLite-specific optimizations
+        connect_args={"check_same_thread": False}
+    )
+else:
+    # PostgreSQL settings (fallback)
+    engine = create_async_engine(
+        database_url,
+        echo=settings.debug,
+        future=True,
+        pool_pre_ping=True,
+        pool_size=5,
+        max_overflow=10
+    )
+
+# Create async session factory
+async_session = async_sessionmaker(
+    engine,
+    class_=AsyncSession,
+    expire_on_commit=False
+)
+
+
+async def get_session() -> AsyncSession:
+    """Dependency to get database session"""
+    async with async_session() as session:
+        yield session